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 $236.30   13.306%   $267.7421   $267.74   $267.75   $267.70  
  Purchase #2 $20.26   10.276%   $22.3419   $22.34   $22.35   $22.30  
  Purchase #3 $91.78   7.445%   $98.613   $98.61   $98.60   $98.60  
  Purchase #4 $60.92   4.860%   $63.8807   $63.88   $63.90   $63.90  
  Purchase #5 $24.51   3.482%   $25.3634   $25.36   $25.35   $25.40  
  Purchase #6 $207.35   9.789%   $227.6475   $227.65   $227.65   $227.60  
  Purchase #7 $169.98   5.103%   $178.6541   $178.65   $178.65   $178.70  
  7 purchase totals = $811.10       $884.2427   $884.23   $884.25   $884.20