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 $44.61   6.501%   $47.5101   $47.51   $47.50   $47.50  
  Purchase #2 $193.27   6.690%   $206.1998   $206.20   $206.20   $206.20  
  Purchase #3 $120.92   8.422%   $131.1039   $131.10   $131.10   $131.10  
  Purchase #4 $137.55   9.599%   $150.7534   $150.75   $150.75   $150.80  
  Purchase #5 $12.65   7.605%   $13.612   $13.61   $13.60   $13.60  
  Purchase #6 $56.39   5.480%   $59.4802   $59.48   $59.50   $59.50  
  Purchase #7 $76.44   13.396%   $86.6799   $86.68   $86.70   $86.70  
  7 purchase totals = $641.83       $695.3393   $695.33   $695.35   $695.40