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 $133.63   6.429%   $142.2211   $142.22   $142.20   $142.20  
  Purchase #2 $183.96   13.677%   $209.1202   $209.12   $209.10   $209.10  
  Purchase #3 $107.58   6.470%   $114.5404   $114.54   $114.55   $114.50  
  Purchase #4 $232.36   11.811%   $259.804   $259.80   $259.80   $259.80  
  Purchase #5 $105.53   3.389%   $109.1064   $109.11   $109.10   $109.10  
  Purchase #6 $145.72   4.856%   $152.7962   $152.80   $152.80   $152.80  
  Purchase #7 $91.54   10.352%   $101.0162   $101.02   $101.00   $101.00  
  7 purchase totals = $1,000.32       $1,088.6045   $1,088.61   $1,088.55   $1,088.50