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 $59.56   6.547%   $63.4594   $63.46   $63.45   $63.50  
  Purchase #2 $127.74   10.381%   $141.0007   $141.00   $141.00   $141.00  
  Purchase #3 $119.28   11.426%   $132.9089   $132.91   $132.90   $132.90  
  Purchase #4 $89.46   8.402%   $96.9764   $96.98   $97.00   $97.00  
  Purchase #5 $111.37   3.809%   $115.6121   $115.61   $115.60   $115.60  
  Purchase #6 $242.80   13.383%   $275.2939   $275.29   $275.30   $275.30  
  Purchase #7 $104.91   8.716%   $114.054   $114.05   $114.05   $114.10  
  7 purchase totals = $855.12       $939.3054   $939.30   $939.30   $939.40