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 $220.82   5.571%   $233.1219   $233.12   $233.10   $233.10  
  Purchase #2 $81.68   6.468%   $86.9631   $86.96   $86.95   $87.00  
  Purchase #3 $10.74   6.192%   $11.405   $11.41   $11.40   $11.40  
  Purchase #4 $98.76   4.422%   $103.1272   $103.13   $103.15   $103.10  
  Purchase #5 $236.42   9.759%   $259.4922   $259.49   $259.50   $259.50  
  Purchase #6 $187.97   10.477%   $207.6636   $207.66   $207.65   $207.70  
  Purchase #7 $126.95   3.541%   $131.4453   $131.45   $131.45   $131.40  
  7 purchase totals = $963.34       $1,033.2183   $1,033.22   $1,033.20   $1,033.20