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 $60.32   6.281%   $64.1087   $64.11   $64.10   $64.10  
  Purchase #2 $197.78   11.717%   $220.9539   $220.95   $220.95   $221.00  
  Purchase #3 $186.43   3.637%   $193.2105   $193.21   $193.20   $193.20  
  Purchase #4 $207.83   7.832%   $224.1072   $224.11   $224.10   $224.10  
  Purchase #5 $49.40   4.383%   $51.5652   $51.57   $51.55   $51.60  
  Purchase #6 $57.73   5.123%   $60.6875   $60.69   $60.70   $60.70  
  Purchase #7 $217.28   11.519%   $242.3085   $242.31   $242.30   $242.30  
  7 purchase totals = $976.77       $1,056.9415   $1,056.95   $1,056.90   $1,057.00