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 $184.40   13.359%   $209.034   $209.03   $209.05   $209.00  
  Purchase #2 $51.93   5.346%   $54.7062   $54.71   $54.70   $54.70  
  Purchase #3 $176.27   11.868%   $197.1897   $197.19   $197.20   $197.20  
  Purchase #4 $43.68   9.636%   $47.889   $47.89   $47.90   $47.90  
  Purchase #5 $63.38   11.701%   $70.7961   $70.80   $70.80   $70.80  
  Purchase #6 $111.85   13.403%   $126.8413   $126.84   $126.85   $126.80  
  Purchase #7 $115.55   5.541%   $121.9526   $121.95   $121.95   $122.00  
  7 purchase totals = $747.06       $828.4089   $828.41   $828.45   $828.40