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	$62.40	5.632%	$65.9144	$65.91	$65.90	$65.90
Purchase #2	$42.45	7.710%	$45.7229	$45.72	$45.70	$45.70
Purchase #3	$220.29	3.842%	$228.7535	$228.75	$228.75	$228.80
Purchase #4	$28.98	4.607%	$30.3151	$30.32	$30.30	$30.30
Purchase #5	$105.50	6.519%	$112.3775	$112.38	$112.40	$112.40
Purchase #6	$159.75	6.707%	$170.4644	$170.46	$170.45	$170.50
Purchase #7	$11.92	11.164%	$13.2507	$13.25	$13.25	$13.30
7 purchase totals =	$631.29		$666.7985	$666.79	$666.75	$666.90