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 $41.36   6.747%   $44.1506   $44.15   $44.15   $44.20  
  Purchase #2 $65.81   13.686%   $74.8168   $74.82   $74.80   $74.80  
  Purchase #3 $26.39   6.596%   $28.1307   $28.13   $28.15   $28.10  
  Purchase #4 $222.75   13.331%   $252.4448   $252.44   $252.45   $252.40  
  Purchase #5 $16.44   7.653%   $17.6982   $17.70   $17.70   $17.70  
  Purchase #6 $118.94   5.136%   $125.0488   $125.05   $125.05   $125.00  
  Purchase #7 $126.30   4.514%   $132.0012   $132.00   $132.00   $132.00  
  7 purchase totals = $617.99       $674.2911   $674.29   $674.30   $674.20