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 $60.94   11.766%   $68.1102   $68.11   $68.10   $68.10  
  Purchase #2 $108.71   5.158%   $114.3173   $114.32   $114.30   $114.30  
  Purchase #3 $182.44   6.491%   $194.2822   $194.28   $194.30   $194.30  
  Purchase #4 $131.51   11.670%   $146.8572   $146.86   $146.85   $146.90  
  Purchase #5 $108.78   11.764%   $121.5769   $121.58   $121.60   $121.60  
  Purchase #6 $103.70   10.846%   $114.9473   $114.95   $114.95   $114.90  
  Purchase #7 $160.93   3.828%   $167.0904   $167.09   $167.10   $167.10  
  7 purchase totals = $857.01       $927.1815   $927.19   $927.20   $927.20