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 $149.94   11.597%   $167.3285   $167.33   $167.35   $167.30  
  Purchase #2 $180.69   9.404%   $197.6821   $197.68   $197.70   $197.70  
  Purchase #3 $234.55   10.326%   $258.7696   $258.77   $258.75   $258.80  
  Purchase #4 $193.30   5.353%   $203.6473   $203.65   $203.65   $203.60  
  Purchase #5 $182.34   5.271%   $191.9511   $191.95   $191.95   $192.00  
  Purchase #6 $37.36   13.827%   $42.5258   $42.53   $42.55   $42.50  
  Purchase #7 $228.88   6.792%   $244.4255   $244.43   $244.45   $244.40  
  7 purchase totals = $1,207.06       $1,306.3299   $1,306.34   $1,306.40   $1,306.30