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 $212.33   9.812%   $233.1638   $233.16   $233.15   $233.20  
  Purchase #2 $151.29   7.510%   $162.6519   $162.65   $162.65   $162.70  
  Purchase #3 $205.33   7.633%   $221.0028   $221.00   $221.00   $221.00  
  Purchase #4 $32.97   4.186%   $34.3501   $34.35   $34.35   $34.40  
  Purchase #5 $9.81   8.462%   $10.6401   $10.64   $10.65   $10.60  
  Purchase #6 $148.76   10.643%   $164.5925   $164.59   $164.60   $164.60  
  Purchase #7 $21.48   8.645%   $23.3369   $23.34   $23.35   $23.30  
  7 purchase totals = $781.97       $849.7381   $849.73   $849.75   $849.80