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 $218.54   9.201%   $238.6479   $238.65   $238.65   $238.60  
  Purchase #2 $57.31   9.277%   $62.6266   $62.63   $62.65   $62.60  
  Purchase #3 $68.27   13.824%   $77.7076   $77.71   $77.70   $77.70  
  Purchase #4 $177.54   3.598%   $183.9279   $183.93   $183.95   $183.90  
  Purchase #5 $101.79   13.307%   $115.3352   $115.34   $115.35   $115.30  
  Purchase #6 $208.60   3.738%   $216.3975   $216.40   $216.40   $216.40  
  Purchase #7 $56.70   10.196%   $62.4811   $62.48   $62.50   $62.50  
  7 purchase totals = $888.75       $957.1238   $957.14   $957.20   $957.00