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 $47.84   8.763%   $52.0322   $52.03   $52.05   $52.00  
  Purchase #2 $30.67   13.247%   $34.7329   $34.73   $34.75   $34.70  
  Purchase #3 $96.44   10.661%   $106.7215   $106.72   $106.70   $106.70  
  Purchase #4 $80.61   8.166%   $87.1926   $87.19   $87.20   $87.20  
  Purchase #5 $206.37   4.120%   $214.8724   $214.87   $214.85   $214.90  
  Purchase #6 $146.97   5.127%   $154.5052   $154.51   $154.50   $154.50  
  Purchase #7 $227.65   9.111%   $248.3912   $248.39   $248.40   $248.40  
  7 purchase totals = $836.55       $898.4480   $898.44   $898.45   $898.40