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 $32.43   4.154%   $33.7771   $33.78   $33.80   $33.80  
  Purchase #2 $34.86   4.856%   $36.5528   $36.55   $36.55   $36.60  
  Purchase #3 $55.91   10.699%   $61.8918   $61.89   $61.90   $61.90  
  Purchase #4 $28.87   12.600%   $32.5076   $32.51   $32.50   $32.50  
  Purchase #5 $214.75   5.132%   $225.771   $225.77   $225.75   $225.80  
  Purchase #6 $121.94   9.341%   $133.3304   $133.33   $133.35   $133.30  
  Purchase #7 $177.74   13.677%   $202.0495   $202.05   $202.05   $202.00  
  7 purchase totals = $666.50       $725.8802   $725.88   $725.90   $725.90