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 $244.97   6.298%   $260.3982   $260.40   $260.40   $260.40  
  Purchase #2 $119.57   4.547%   $125.0068   $125.01   $125.00   $125.00  
  Purchase #3 $118.27   3.633%   $122.5667   $122.57   $122.55   $122.60  
  Purchase #4 $138.72   13.323%   $157.2017   $157.20   $157.20   $157.20  
  Purchase #5 $247.47   11.201%   $275.1891   $275.19   $275.20   $275.20  
  Purchase #6 $230.83   5.610%   $243.7796   $243.78   $243.80   $243.80  
  Purchase #7 $151.89   12.853%   $171.4124   $171.41   $171.40   $171.40  
  7 purchase totals = $1,251.72       $1,355.5545   $1,355.56   $1,355.55   $1,355.60