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 $61.39   10.164%   $67.6297   $67.63   $67.65   $67.60  
  Purchase #2 $124.81   12.622%   $140.5635   $140.56   $140.55   $140.60  
  Purchase #3 $126.56   10.803%   $140.2323   $140.23   $140.25   $140.20  
  Purchase #4 $62.70   12.424%   $70.4898   $70.49   $70.50   $70.50  
  Purchase #5 $171.43   7.495%   $184.2787   $184.28   $184.30   $184.30  
  Purchase #6 $54.87   6.104%   $58.2193   $58.22   $58.20   $58.20  
  Purchase #7 $31.94   12.863%   $36.0484   $36.05   $36.05   $36.00  
  7 purchase totals = $633.70       $697.4617   $697.46   $697.50   $697.40