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	$250.79	11.760%	$280.2829	$280.28	$280.30	$280.30
Purchase #2	$121.98	5.742%	$128.9841	$128.98	$129.00	$129.00
Purchase #3	$106.89	4.707%	$111.9213	$111.92	$111.90	$111.90
Purchase #4	$66.67	8.776%	$72.521	$72.52	$72.50	$72.50
Purchase #5	$130.48	6.685%	$139.2026	$139.20	$139.20	$139.20
Purchase #6	$140.91	6.103%	$149.5097	$149.51	$149.50	$149.50
Purchase #7	$30.72	8.551%	$33.3469	$33.35	$33.35	$33.30
7 purchase totals =	$848.44		$915.7685	$915.76	$915.75	$915.70