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 $241.87   8.251%   $261.8267   $261.83   $261.85   $261.80  
  Purchase #2 $193.50   6.767%   $206.5941   $206.59   $206.60   $206.60  
  Purchase #3 $92.94   9.473%   $101.7442   $101.74   $101.75   $101.70  
  Purchase #4 $244.75   5.717%   $258.7424   $258.74   $258.75   $258.70  
  Purchase #5 $230.57   13.195%   $260.9937   $260.99   $261.00   $261.00  
  Purchase #6 $124.58   13.267%   $141.108   $141.11   $141.10   $141.10  
  Purchase #7 $219.97   7.631%   $236.7559   $236.76   $236.75   $236.80  
  7 purchase totals = $1,348.18       $1,467.7650   $1,467.76   $1,467.80   $1,467.70