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 $26.74   9.536%   $29.2899   $29.29   $29.30   $29.30  
  Purchase #2 $47.46   5.201%   $49.9284   $49.93   $49.95   $49.90  
  Purchase #3 $54.63   5.155%   $57.4462   $57.45   $57.45   $57.40  
  Purchase #4 $62.86   13.596%   $71.4064   $71.41   $71.40   $71.40  
  Purchase #5 $209.99   10.367%   $231.7597   $231.76   $231.75   $231.80  
  Purchase #6 $78.86   5.228%   $82.9828   $82.98   $83.00   $83.00  
  Purchase #7 $244.60   6.315%   $260.0465   $260.05   $260.05   $260.00  
  7 purchase totals = $725.14       $782.8599   $782.87   $782.90   $782.80