Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $104.81   12.831%   $118.2582   $118.26   $118.25   $118.30  
  Purchase #2 $247.76   5.460%   $261.2877   $261.29   $261.30   $261.30  
  Purchase #3 $118.79   8.312%   $128.6638   $128.66   $128.65   $128.70  
  Purchase #4 $182.37   5.432%   $192.2763   $192.28   $192.30   $192.30  
  Purchase #5 $219.42   9.550%   $240.3746   $240.37   $240.35   $240.40  
  Purchase #6 $107.39   9.506%   $117.5985   $117.60   $117.60   $117.60  
  Purchase #7 $245.55   3.320%   $253.7023   $253.70   $253.70   $253.70  
  7 purchase totals = $1,226.09       $1,312.1614   $1,312.16   $1,312.15   $1,312.30