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 $61.87   6.752%   $66.0475   $66.05   $66.05   $66.00  
  Purchase #2 $117.32   11.797%   $131.1602   $131.16   $131.15   $131.20  
  Purchase #3 $35.75   12.590%   $40.2509   $40.25   $40.25   $40.30  
  Purchase #4 $116.94   8.412%   $126.777   $126.78   $126.80   $126.80  
  Purchase #5 $114.69   11.733%   $128.1466   $128.15   $128.15   $128.10  
  Purchase #6 $121.59   11.734%   $135.8574   $135.86   $135.85   $135.90  
  Purchase #7 $193.40   7.298%   $207.5143   $207.51   $207.50   $207.50  
  7 purchase totals = $761.56       $835.7539   $835.76   $835.75   $835.80