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 $94.47   10.248%   $104.1513   $104.15   $104.15   $104.20  
  Purchase #2 $144.41   13.131%   $163.3725   $163.37   $163.35   $163.40  
  Purchase #3 $73.35   11.641%   $81.8887   $81.89   $81.90   $81.90  
  Purchase #4 $222.42   6.763%   $237.4623   $237.46   $237.45   $237.50  
  Purchase #5 $55.36   4.452%   $57.8246   $57.82   $57.80   $57.80  
  Purchase #6 $95.53   12.567%   $107.5353   $107.54   $107.55   $107.50  
  Purchase #7 $41.85   7.458%   $44.9712   $44.97   $44.95   $45.00  
  7 purchase totals = $727.39       $797.2059   $797.20   $797.15   $797.30