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 $226.59   5.718%   $239.5464   $239.55   $239.55   $239.50  
  Purchase #2 $189.78   3.304%   $196.0503   $196.05   $196.05   $196.10  
  Purchase #3 $88.47   7.357%   $94.9787   $94.98   $95.00   $95.00  
  Purchase #4 $59.75   6.252%   $63.4856   $63.49   $63.50   $63.50  
  Purchase #5 $104.66   5.251%   $110.1557   $110.16   $110.15   $110.20  
  Purchase #6 $92.48   10.836%   $102.5011   $102.50   $102.50   $102.50  
  Purchase #7 $84.46   12.580%   $95.0851   $95.09   $95.10   $95.10  
  7 purchase totals = $846.19       $901.8029   $901.82   $901.85   $901.90