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 $92.69   12.362%   $104.1483   $104.15   $104.15   $104.10  
  Purchase #2 $95.73   13.290%   $108.4525   $108.45   $108.45   $108.50  
  Purchase #3 $143.98   12.201%   $161.547   $161.55   $161.55   $161.50  
  Purchase #4 $152.30   11.422%   $169.6957   $169.70   $169.70   $169.70  
  Purchase #5 $173.36   5.495%   $182.8861   $182.89   $182.90   $182.90  
  Purchase #6 $187.50   10.559%   $207.2981   $207.30   $207.30   $207.30  
  Purchase #7 $36.57   5.673%   $38.6446   $38.64   $38.65   $38.60  
  7 purchase totals = $882.13       $972.6723   $972.68   $972.70   $972.60