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 $113.99   3.654%   $118.1552   $118.16   $118.15   $118.20  
  Purchase #2 $44.46   9.796%   $48.8153   $48.82   $48.80   $48.80  
  Purchase #3 $65.26   12.180%   $73.2087   $73.21   $73.20   $73.20  
  Purchase #4 $206.25   13.271%   $233.6214   $233.62   $233.60   $233.60  
  Purchase #5 $183.98   6.192%   $195.372   $195.37   $195.35   $195.40  
  Purchase #6 $131.75   4.453%   $137.6168   $137.62   $137.60   $137.60  
  Purchase #7 $51.83   4.250%   $54.0328   $54.03   $54.05   $54.00  
  7 purchase totals = $797.52       $860.8222   $860.83   $860.75   $860.80