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 $115.31   9.593%   $126.3717   $126.37   $126.35   $126.40  
  Purchase #2 $47.43   12.334%   $53.28   $53.28   $53.30   $53.30  
  Purchase #3 $201.28   9.749%   $220.9028   $220.90   $220.90   $220.90  
  Purchase #4 $32.78   5.306%   $34.5193   $34.52   $34.50   $34.50  
  Purchase #5 $106.58   10.483%   $117.7528   $117.75   $117.75   $117.80  
  Purchase #6 $23.99   11.412%   $26.7277   $26.73   $26.75   $26.70  
  Purchase #7 $186.60   4.316%   $194.6537   $194.65   $194.65   $194.70  
  7 purchase totals = $713.97       $774.2080   $774.20   $774.20   $774.30