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 $215.32   13.606%   $244.6164   $244.62   $244.60   $244.60  
  Purchase #2 $234.51   7.746%   $252.6751   $252.68   $252.70   $252.70  
  Purchase #3 $58.79   7.228%   $63.0393   $63.04   $63.05   $63.00  
  Purchase #4 $195.91   7.222%   $210.0586   $210.06   $210.05   $210.10  
  Purchase #5 $230.42   11.577%   $257.0957   $257.10   $257.10   $257.10  
  Purchase #6 $118.65   10.741%   $131.3942   $131.39   $131.40   $131.40  
  Purchase #7 $118.54   6.208%   $125.899   $125.90   $125.90   $125.90  
  7 purchase totals = $1,172.14       $1,284.7783   $1,284.79   $1,284.80   $1,284.80