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	$171.25	8.204%	$185.2994	$185.30	$185.30	$185.30
Purchase #2	$66.48	11.689%	$74.2508	$74.25	$74.25	$74.30
Purchase #3	$99.46	5.145%	$104.5772	$104.58	$104.60	$104.60
Purchase #4	$131.62	4.255%	$137.2204	$137.22	$137.20	$137.20
Purchase #5	$36.61	13.136%	$41.4191	$41.42	$41.40	$41.40
Purchase #6	$63.94	12.798%	$72.123	$72.12	$72.10	$72.10
Purchase #7	$69.95	7.218%	$74.999	$75.00	$75.00	$75.00
7 purchase totals =	$639.31		$689.8889	$689.89	$689.85	$689.90