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 $154.73   9.142%   $168.8754   $168.88   $168.90   $168.90  
  Purchase #2 $47.82   13.567%   $54.3077   $54.31   $54.30   $54.30  
  Purchase #3 $66.80   10.179%   $73.5996   $73.60   $73.60   $73.60  
  Purchase #4 $116.68   8.502%   $126.6001   $126.60   $126.60   $126.60  
  Purchase #5 $218.85   5.814%   $231.5739   $231.57   $231.55   $231.60  
  Purchase #6 $189.38   6.565%   $201.8128   $201.81   $201.80   $201.80  
  Purchase #7 $47.57   3.487%   $49.2288   $49.23   $49.25   $49.20  
  7 purchase totals = $841.83       $905.9983   $906.00   $906.00   $906.00