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 $30.58   9.134%   $33.3732   $33.37   $33.35   $33.40  
  Purchase #2 $83.92   11.830%   $93.8477   $93.85   $93.85   $93.80  
  Purchase #3 $106.59   7.606%   $114.6972   $114.70   $114.70   $114.70  
  Purchase #4 $35.41   5.338%   $37.3002   $37.30   $37.30   $37.30  
  Purchase #5 $115.43   10.621%   $127.6898   $127.69   $127.70   $127.70  
  Purchase #6 $169.91   13.815%   $193.3831   $193.38   $193.40   $193.40  
  Purchase #7 $48.50   8.180%   $52.4673   $52.47   $52.45   $52.50  
  7 purchase totals = $590.34       $652.7585   $652.76   $652.75   $652.80