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 $238.91   10.421%   $263.8068   $263.81   $263.80   $263.80  
  Purchase #2 $104.72   8.826%   $113.9626   $113.96   $113.95   $114.00  
  Purchase #3 $86.48   11.471%   $96.4001   $96.40   $96.40   $96.40  
  Purchase #4 $248.31   9.139%   $271.0031   $271.00   $271.00   $271.00  
  Purchase #5 $86.31   9.206%   $94.2557   $94.26   $94.25   $94.30  
  Purchase #6 $38.83   5.240%   $40.8647   $40.86   $40.85   $40.90  
  Purchase #7 $42.44   13.747%   $48.2742   $48.27   $48.25   $48.30  
  7 purchase totals = $846.00       $928.5672   $928.56   $928.50   $928.70