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 $192.81   8.412%   $209.0292   $209.03   $209.05   $209.00  
  Purchase #2 $59.49   8.733%   $64.6853   $64.69   $64.70   $64.70  
  Purchase #3 $218.33   12.271%   $245.1213   $245.12   $245.10   $245.10  
  Purchase #4 $202.38   9.336%   $221.2742   $221.27   $221.25   $221.30  
  Purchase #5 $165.70   5.297%   $174.4771   $174.48   $174.50   $174.50  
  Purchase #6 $38.45   8.229%   $41.6141   $41.61   $41.60   $41.60  
  Purchase #7 $249.86   11.597%   $278.8363   $278.84   $278.85   $278.80  
  7 purchase totals = $1,127.02       $1,235.0375   $1,235.04   $1,235.05   $1,235.00