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 $58.40   8.417%   $63.3155   $63.32   $63.30   $63.30  
  Purchase #2 $212.27   7.724%   $228.6657   $228.67   $228.65   $228.70  
  Purchase #3 $150.89   7.637%   $162.4135   $162.41   $162.40   $162.40  
  Purchase #4 $55.55   9.586%   $60.875   $60.88   $60.90   $60.90  
  Purchase #5 $125.41   4.596%   $131.1738   $131.17   $131.15   $131.20  
  Purchase #6 $90.70   11.475%   $101.1078   $101.11   $101.10   $101.10  
  Purchase #7 $75.29   8.874%   $81.9712   $81.97   $81.95   $82.00  
  7 purchase totals = $768.51       $829.5225   $829.53   $829.45   $829.60