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 $56.25   11.494%   $62.7154   $62.72   $62.70   $62.70  
  Purchase #2 $142.67   11.144%   $158.5691   $158.57   $158.55   $158.60  
  Purchase #3 $120.82   10.766%   $133.8275   $133.83   $133.85   $133.80  
  Purchase #4 $163.86   11.392%   $182.5269   $182.53   $182.55   $182.50  
  Purchase #5 $207.96   12.709%   $234.3896   $234.39   $234.40   $234.40  
  Purchase #6 $121.96   9.311%   $133.3157   $133.32   $133.30   $133.30  
  Purchase #7 $75.60   8.827%   $82.2732   $82.27   $82.25   $82.30  
  7 purchase totals = $889.12       $987.6174   $987.63   $987.60   $987.60