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 $60.88   12.517%   $68.5003   $68.50   $68.50   $68.50  
  Purchase #2 $140.93   5.873%   $149.2068   $149.21   $149.20   $149.20  
  Purchase #3 $116.92   7.114%   $125.2377   $125.24   $125.25   $125.20  
  Purchase #4 $167.91   7.775%   $180.965   $180.97   $180.95   $181.00  
  Purchase #5 $161.52   8.287%   $174.9052   $174.91   $174.90   $174.90  
  Purchase #6 $8.47   11.790%   $9.4686   $9.47   $9.45   $9.50  
  Purchase #7 $111.68   12.326%   $125.4457   $125.45   $125.45   $125.40  
  7 purchase totals = $768.31       $833.7293   $833.75   $833.70   $833.70