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 $112.60   11.386%   $125.4206   $125.42   $125.40   $125.40  
  Purchase #2 $140.54   6.196%   $149.2479   $149.25   $149.25   $149.20  
  Purchase #3 $244.95   12.129%   $274.66   $274.66   $274.65   $274.70  
  Purchase #4 $143.76   5.595%   $151.8034   $151.80   $151.80   $151.80  
  Purchase #5 $67.36   7.249%   $72.2429   $72.24   $72.25   $72.20  
  Purchase #6 $54.32   3.135%   $56.0229   $56.02   $56.00   $56.00  
  Purchase #7 $165.28   12.521%   $185.9747   $185.97   $185.95   $186.00  
  7 purchase totals = $928.81       $1,015.3724   $1,015.36   $1,015.30   $1,015.30