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 $56.62   5.516%   $59.7432   $59.74   $59.75   $59.70  
  Purchase #2 $169.47   8.196%   $183.3598   $183.36   $183.35   $183.40  
  Purchase #3 $115.26   8.606%   $125.1793   $125.18   $125.20   $125.20  
  Purchase #4 $13.56   7.211%   $14.5378   $14.54   $14.55   $14.50  
  Purchase #5 $9.93   9.198%   $10.8434   $10.84   $10.85   $10.80  
  Purchase #6 $248.45   7.258%   $266.4825   $266.48   $266.50   $266.50  
  Purchase #7 $222.68   4.668%   $233.0747   $233.07   $233.05   $233.10  
  7 purchase totals = $835.97       $893.2207   $893.21   $893.25   $893.20