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 $236.66   7.372%   $254.1066   $254.11   $254.10   $254.10  
  Purchase #2 $76.63   13.486%   $86.9643   $86.96   $86.95   $87.00  
  Purchase #3 $119.38   3.869%   $123.9988   $124.00   $124.00   $124.00  
  Purchase #4 $60.95   7.176%   $65.3238   $65.32   $65.30   $65.30  
  Purchase #5 $52.77   6.320%   $56.1051   $56.11   $56.10   $56.10  
  Purchase #6 $60.53   9.838%   $66.4849   $66.48   $66.50   $66.50  
  Purchase #7 $124.38   11.768%   $139.017   $139.02   $139.00   $139.00  
  7 purchase totals = $731.30       $792.0005   $792.00   $791.95   $792.00