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 $202.82   3.343%   $209.6003   $209.60   $209.60   $209.60  
  Purchase #2 $21.81   6.826%   $23.2988   $23.30   $23.30   $23.30  
  Purchase #3 $95.48   3.847%   $99.1531   $99.15   $99.15   $99.20  
  Purchase #4 $179.49   3.176%   $185.1906   $185.19   $185.20   $185.20  
  Purchase #5 $210.44   13.234%   $238.2896   $238.29   $238.30   $238.30  
  Purchase #6 $77.36   7.817%   $83.4072   $83.41   $83.40   $83.40  
  Purchase #7 $106.28   6.722%   $113.4241   $113.42   $113.40   $113.40  
  7 purchase totals = $893.68       $952.3637   $952.36   $952.35   $952.40