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 $87.48   10.413%   $96.5893   $96.59   $96.60   $96.60  
  Purchase #2 $239.55   8.244%   $259.2985   $259.30   $259.30   $259.30  
  Purchase #3 $93.29   8.189%   $100.9295   $100.93   $100.95   $100.90  
  Purchase #4 $199.75   3.539%   $206.8192   $206.82   $206.80   $206.80  
  Purchase #5 $72.41   3.274%   $74.7807   $74.78   $74.80   $74.80  
  Purchase #6 $202.56   7.285%   $217.3165   $217.32   $217.30   $217.30  
  Purchase #7 $37.38   9.853%   $41.0631   $41.06   $41.05   $41.10  
  7 purchase totals = $932.42       $996.7968   $996.80   $996.80   $996.80