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 $206.53   12.394%   $232.1273   $232.13   $232.15   $232.10  
  Purchase #2 $142.75   3.559%   $147.8305   $147.83   $147.85   $147.80  
  Purchase #3 $85.34   12.459%   $95.9725   $95.97   $95.95   $96.00  
  Purchase #4 $28.99   8.608%   $31.4855   $31.49   $31.50   $31.50  
  Purchase #5 $179.69   4.234%   $187.2981   $187.30   $187.30   $187.30  
  Purchase #6 $159.74   5.579%   $168.6519   $168.65   $168.65   $168.70  
  Purchase #7 $192.49   7.274%   $206.4917   $206.49   $206.50   $206.50  
  7 purchase totals = $995.53       $1,069.8575   $1,069.86   $1,069.90   $1,069.90