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 $149.84   9.114%   $163.4964   $163.50   $163.50   $163.50  
  Purchase #2 $15.27   6.419%   $16.2502   $16.25   $16.25   $16.30  
  Purchase #3 $201.75   4.182%   $210.1872   $210.19   $210.20   $210.20  
  Purchase #4 $136.46   12.595%   $153.6471   $153.65   $153.65   $153.60  
  Purchase #5 $53.83   11.758%   $60.1593   $60.16   $60.15   $60.20  
  Purchase #6 $14.28   9.419%   $15.625   $15.63   $15.65   $15.60  
  Purchase #7 $100.41   13.221%   $113.6852   $113.69   $113.70   $113.70  
  7 purchase totals = $671.84       $733.0504   $733.07   $733.10   $733.10