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 $23.30   5.490%   $24.5792   $24.58   $24.60   $24.60  
  Purchase #2 $156.69   7.320%   $168.1597   $168.16   $168.15   $168.20  
  Purchase #3 $168.43   5.257%   $177.2844   $177.28   $177.30   $177.30  
  Purchase #4 $155.61   9.617%   $170.575   $170.58   $170.60   $170.60  
  Purchase #5 $87.85   5.698%   $92.8557   $92.86   $92.85   $92.90  
  Purchase #6 $210.58   5.341%   $221.8271   $221.83   $221.85   $221.80  
  Purchase #7 $180.73   7.870%   $194.9535   $194.95   $194.95   $195.00  
  7 purchase totals = $983.19       $1,050.2346   $1,050.24   $1,050.30   $1,050.40