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 $241.47   10.780%   $267.5005   $267.50   $267.50   $267.50  
  Purchase #2 $45.90   8.564%   $49.8309   $49.83   $49.85   $49.80  
  Purchase #3 $112.90   9.804%   $123.9687   $123.97   $123.95   $124.00  
  Purchase #4 $83.97   11.384%   $93.5291   $93.53   $93.55   $93.50  
  Purchase #5 $177.94   3.507%   $184.1804   $184.18   $184.20   $184.20  
  Purchase #6 $42.60   9.726%   $46.7433   $46.74   $46.75   $46.70  
  Purchase #7 $219.47   8.395%   $237.8945   $237.89   $237.90   $237.90  
  7 purchase totals = $924.25       $1,003.6474   $1,003.64   $1,003.70   $1,003.60