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	$6.32	8.534%	$6.8593	$6.86	$6.85	$6.90
Purchase #2	$229.62	11.870%	$256.8759	$256.88	$256.90	$256.90
Purchase #3	$133.67	4.111%	$139.1652	$139.17	$139.15	$139.20
Purchase #4	$221.92	10.849%	$245.9961	$246.00	$246.00	$246.00
Purchase #5	$83.46	11.181%	$92.7917	$92.79	$92.80	$92.80
Purchase #6	$143.43	9.366%	$156.8637	$156.86	$156.85	$156.90
Purchase #7	$152.64	11.583%	$170.3203	$170.32	$170.30	$170.30
7 purchase totals =	$971.06		$1,068.8722	$1,068.88	$1,068.85	$1,069.00