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 $58.63   10.189%   $64.6038   $64.60   $64.60   $64.60  
  Purchase #2 $63.81   3.372%   $65.9617   $65.96   $65.95   $66.00  
  Purchase #3 $191.29   13.389%   $216.9018   $216.90   $216.90   $216.90  
  Purchase #4 $124.97   3.846%   $129.7763   $129.78   $129.80   $129.80  
  Purchase #5 $220.99   10.543%   $244.289   $244.29   $244.30   $244.30  
  Purchase #6 $103.61   12.589%   $116.6535   $116.65   $116.65   $116.70  
  Purchase #7 $129.58   5.240%   $136.37   $136.37   $136.35   $136.40  
  7 purchase totals = $892.88       $974.5561   $974.55   $974.55   $974.70