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 $249.83   8.708%   $271.5852   $271.59   $271.60   $271.60  
  Purchase #2 $200.82   13.378%   $227.6857   $227.69   $227.70   $227.70  
  Purchase #3 $92.41   5.583%   $97.5693   $97.57   $97.55   $97.60  
  Purchase #4 $7.78   12.392%   $8.7441   $8.74   $8.75   $8.70  
  Purchase #5 $204.48   11.367%   $227.7232   $227.72   $227.70   $227.70  
  Purchase #6 $143.95   11.632%   $160.6943   $160.69   $160.70   $160.70  
  Purchase #7 $63.89   5.198%   $67.211   $67.21   $67.20   $67.20  
  7 purchase totals = $963.16       $1,061.2128   $1,061.21   $1,061.20   $1,061.20