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 $59.59   12.247%   $66.888   $66.89   $66.90   $66.90  
  Purchase #2 $33.41   6.602%   $35.6157   $35.62   $35.60   $35.60  
  Purchase #3 $224.78   9.534%   $246.2105   $246.21   $246.20   $246.20  
  Purchase #4 $214.53   10.346%   $236.7253   $236.73   $236.75   $236.70  
  Purchase #5 $179.93   8.148%   $194.5907   $194.59   $194.60   $194.60  
  Purchase #6 $202.79   9.215%   $221.4771   $221.48   $221.50   $221.50  
  Purchase #7 $177.68   11.311%   $197.7774   $197.78   $197.80   $197.80  
  7 purchase totals = $1,092.71       $1,199.2847   $1,199.30   $1,199.35   $1,199.30