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 $74.47   11.801%   $83.2582   $83.26   $83.25   $83.30  
  Purchase #2 $83.72   12.308%   $94.0243   $94.02   $94.00   $94.00  
  Purchase #3 $112.65   7.189%   $120.7484   $120.75   $120.75   $120.70  
  Purchase #4 $69.73   13.270%   $78.9832   $78.98   $79.00   $79.00  
  Purchase #5 $188.55   4.763%   $197.5306   $197.53   $197.55   $197.50  
  Purchase #6 $226.71   4.717%   $237.4039   $237.40   $237.40   $237.40  
  Purchase #7 $187.48   13.162%   $212.1561   $212.16   $212.15   $212.20  
  7 purchase totals = $943.31       $1,024.1047   $1,024.10   $1,024.10   $1,024.10