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 $219.43   4.629%   $229.5874   $229.59   $229.60   $229.60  
  Purchase #2 $151.61   7.624%   $163.1687   $163.17   $163.15   $163.20  
  Purchase #3 $148.98   7.552%   $160.231   $160.23   $160.25   $160.20  
  Purchase #4 $165.44   7.361%   $177.618   $177.62   $177.60   $177.60  
  Purchase #5 $234.84   10.381%   $259.2187   $259.22   $259.20   $259.20  
  Purchase #6 $244.78   4.543%   $255.9004   $255.90   $255.90   $255.90  
  Purchase #7 $183.55   7.815%   $197.8944   $197.89   $197.90   $197.90  
  7 purchase totals = $1,348.63       $1,443.6186   $1,443.62   $1,443.60   $1,443.60