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 $184.43   4.140%   $192.0654   $192.07   $192.05   $192.10  
  Purchase #2 $123.86   13.204%   $140.2145   $140.21   $140.20   $140.20  
  Purchase #3 $97.51   4.183%   $101.5888   $101.59   $101.60   $101.60  
  Purchase #4 $14.57   9.126%   $15.8997   $15.90   $15.90   $15.90  
  Purchase #5 $64.87   4.843%   $68.0117   $68.01   $68.00   $68.00  
  Purchase #6 $139.74   6.608%   $148.974   $148.97   $148.95   $149.00  
  Purchase #7 $239.95   8.742%   $260.9264   $260.93   $260.95   $260.90  
  7 purchase totals = $864.93       $927.6805   $927.68   $927.65   $927.70