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 $63.57   8.575%   $69.0211   $69.02   $69.00   $69.00  
  Purchase #2 $213.27   5.428%   $224.8463   $224.85   $224.85   $224.80  
  Purchase #3 $138.92   7.474%   $149.3029   $149.30   $149.30   $149.30  
  Purchase #4 $87.79   11.624%   $97.9947   $97.99   $98.00   $98.00  
  Purchase #5 $116.32   4.307%   $121.3299   $121.33   $121.35   $121.30  
  Purchase #6 $70.63   9.394%   $77.265   $77.27   $77.25   $77.30  
  Purchase #7 $25.50   10.398%   $28.1515   $28.15   $28.15   $28.20  
  7 purchase totals = $716.00       $767.9114   $767.91   $767.90   $767.90