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 $96.74   11.245%   $107.6184   $107.62   $107.60   $107.60  
  Purchase #2 $126.79   3.742%   $131.5345   $131.53   $131.55   $131.50  
  Purchase #3 $28.79   11.215%   $32.0188   $32.02   $32.00   $32.00  
  Purchase #4 $92.43   13.124%   $104.5605   $104.56   $104.55   $104.60  
  Purchase #5 $75.80   11.631%   $84.6163   $84.62   $84.60   $84.60  
  Purchase #6 $116.64   4.853%   $122.3005   $122.30   $122.30   $122.30  
  Purchase #7 $13.60   8.417%   $14.7447   $14.74   $14.75   $14.70  
  7 purchase totals = $550.79       $597.3937   $597.39   $597.35   $597.30