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 $61.77   11.204%   $68.6907   $68.69   $68.70   $68.70  
  Purchase #2 $188.64   3.349%   $194.9576   $194.96   $194.95   $195.00  
  Purchase #3 $243.57   5.493%   $256.9493   $256.95   $256.95   $256.90  
  Purchase #4 $157.45   12.286%   $176.7943   $176.79   $176.80   $176.80  
  Purchase #5 $29.91   4.726%   $31.3235   $31.32   $31.30   $31.30  
  Purchase #6 $27.56   7.519%   $29.6322   $29.63   $29.65   $29.60  
  Purchase #7 $60.29   5.223%   $63.4389   $63.44   $63.45   $63.40  
  7 purchase totals = $769.19       $821.7865   $821.78   $821.80   $821.70