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 $64.96   5.532%   $68.5536   $68.55   $68.55   $68.60  
  Purchase #2 $241.79   5.787%   $255.7824   $255.78   $255.80   $255.80  
  Purchase #3 $164.95   3.138%   $170.1261   $170.13   $170.15   $170.10  
  Purchase #4 $169.76   8.510%   $184.2066   $184.21   $184.20   $184.20  
  Purchase #5 $179.70   12.362%   $201.9145   $201.91   $201.90   $201.90  
  Purchase #6 $137.72   12.175%   $154.4874   $154.49   $154.50   $154.50  
  Purchase #7 $239.68   3.554%   $248.1982   $248.20   $248.20   $248.20  
  7 purchase totals = $1,198.56       $1,283.2688   $1,283.27   $1,283.30   $1,283.30