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 $200.83   8.791%   $218.485   $218.49   $218.50   $218.50  
  Purchase #2 $81.70   4.834%   $85.6494   $85.65   $85.65   $85.60  
  Purchase #3 $100.84   5.285%   $106.1694   $106.17   $106.15   $106.20  
  Purchase #4 $70.66   6.506%   $75.2571   $75.26   $75.25   $75.30  
  Purchase #5 $157.47   7.573%   $169.3952   $169.40   $169.40   $169.40  
  Purchase #6 $65.58   12.662%   $73.8837   $73.88   $73.90   $73.90  
  Purchase #7 $214.50   8.785%   $233.3438   $233.34   $233.35   $233.30  
  7 purchase totals = $891.58       $962.1836   $962.19   $962.20   $962.20