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 $208.36   7.590%   $224.1745   $224.17   $224.15   $224.20  
  Purchase #2 $37.76   11.692%   $42.1749   $42.17   $42.15   $42.20  
  Purchase #3 $22.72   11.478%   $25.3278   $25.33   $25.35   $25.30  
  Purchase #4 $201.48   10.769%   $223.1774   $223.18   $223.20   $223.20  
  Purchase #5 $32.54   7.386%   $34.9434   $34.94   $34.95   $34.90  
  Purchase #6 $163.41   5.261%   $172.007   $172.01   $172.00   $172.00  
  Purchase #7 $218.66   5.653%   $231.0208   $231.02   $231.00   $231.00  
  7 purchase totals = $884.93       $952.8258   $952.82   $952.80   $952.80