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 $59.71   7.182%   $63.9984   $64.00   $64.00   $64.00  
  Purchase #2 $232.26   4.622%   $242.9951   $243.00   $243.00   $243.00  
  Purchase #3 $123.69   10.451%   $136.6168   $136.62   $136.60   $136.60  
  Purchase #4 $232.42   8.449%   $252.0572   $252.06   $252.05   $252.10  
  Purchase #5 $67.62   11.405%   $75.3321   $75.33   $75.35   $75.30  
  Purchase #6 $244.62   8.630%   $265.7307   $265.73   $265.75   $265.70  
  Purchase #7 $237.83   4.745%   $249.115   $249.12   $249.10   $249.10  
  7 purchase totals = $1,198.15       $1,285.8453   $1,285.86   $1,285.85   $1,285.80