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 $234.87   11.141%   $261.0369   $261.04   $261.05   $261.00  
  Purchase #2 $6.83   4.874%   $7.1629   $7.16   $7.15   $7.20  
  Purchase #3 $201.39   11.512%   $224.574   $224.57   $224.55   $224.60  
  Purchase #4 $118.44   12.787%   $133.5849   $133.58   $133.60   $133.60  
  Purchase #5 $10.55   10.306%   $11.6373   $11.64   $11.65   $11.60  
  Purchase #6 $184.83   9.747%   $202.8454   $202.85   $202.85   $202.80  
  Purchase #7 $234.35   5.565%   $247.3916   $247.39   $247.40   $247.40  
  7 purchase totals = $991.26       $1,088.2330   $1,088.23   $1,088.25   $1,088.20