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 $36.46   4.104%   $37.9563   $37.96   $37.95   $38.00  
  Purchase #2 $48.84   6.861%   $52.1909   $52.19   $52.20   $52.20  
  Purchase #3 $212.75   7.783%   $229.3083   $229.31   $229.30   $229.30  
  Purchase #4 $16.57   6.382%   $17.6275   $17.63   $17.65   $17.60  
  Purchase #5 $130.59   13.542%   $148.2745   $148.27   $148.25   $148.30  
  Purchase #6 $223.83   6.727%   $238.887   $238.89   $238.90   $238.90  
  Purchase #7 $208.94   7.200%   $223.9837   $223.98   $224.00   $224.00  
  7 purchase totals = $877.98       $948.2282   $948.23   $948.25   $948.30