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 $91.81   11.518%   $102.3847   $102.38   $102.40   $102.40  
  Purchase #2 $242.78   4.767%   $254.3533   $254.35   $254.35   $254.40  
  Purchase #3 $237.93   12.204%   $266.967   $266.97   $266.95   $267.00  
  Purchase #4 $192.77   10.721%   $213.4369   $213.44   $213.45   $213.40  
  Purchase #5 $247.91   5.559%   $261.6913   $261.69   $261.70   $261.70  
  Purchase #6 $242.31   9.495%   $265.3173   $265.32   $265.30   $265.30  
  Purchase #7 $112.79   5.690%   $119.2078   $119.21   $119.20   $119.20  
  7 purchase totals = $1,368.30       $1,483.3583   $1,483.36   $1,483.35   $1,483.40