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 $83.43   10.593%   $92.2677   $92.27   $92.25   $92.30  
  Purchase #2 $113.53   5.307%   $119.555   $119.56   $119.55   $119.60  
  Purchase #3 $242.97   11.225%   $270.2434   $270.24   $270.25   $270.20  
  Purchase #4 $129.79   12.575%   $146.1111   $146.11   $146.10   $146.10  
  Purchase #5 $228.97   13.615%   $260.1443   $260.14   $260.15   $260.10  
  Purchase #6 $207.32   11.809%   $231.8024   $231.80   $231.80   $231.80  
  Purchase #7 $192.45   6.144%   $204.2741   $204.27   $204.25   $204.30  
  7 purchase totals = $1,198.46       $1,324.3980   $1,324.39   $1,324.35   $1,324.40