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 $34.66   3.354%   $35.8225   $35.82   $35.80   $35.80  
  Purchase #2 $212.94   6.729%   $227.2687   $227.27   $227.25   $227.30  
  Purchase #3 $101.89   12.781%   $114.9126   $114.91   $114.90   $114.90  
  Purchase #4 $239.54   11.841%   $267.9039   $267.90   $267.90   $267.90  
  Purchase #5 $7.73   3.361%   $7.9898   $7.99   $8.00   $8.00  
  Purchase #6 $110.40   4.146%   $114.9772   $114.98   $115.00   $115.00  
  Purchase #7 $132.72   3.502%   $137.3679   $137.37   $137.35   $137.40  
  7 purchase totals = $839.88       $906.2426   $906.24   $906.20   $906.30