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 $61.66   10.652%   $68.228   $68.23   $68.25   $68.20  
  Purchase #2 $125.91   5.790%   $133.2002   $133.20   $133.20   $133.20  
  Purchase #3 $154.94   9.607%   $169.8251   $169.83   $169.85   $169.80  
  Purchase #4 $132.28   6.264%   $140.566   $140.57   $140.55   $140.60  
  Purchase #5 $72.50   6.599%   $77.2843   $77.28   $77.30   $77.30  
  Purchase #6 $106.61   13.746%   $121.2646   $121.26   $121.25   $121.30  
  Purchase #7 $160.32   7.266%   $171.9689   $171.97   $171.95   $172.00  
  7 purchase totals = $814.22       $882.3371   $882.34   $882.35   $882.40