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	$100.46	10.813%	$111.3227	$111.32	$111.30	$111.30
Purchase #2	$5.54	5.236%	$5.8301	$5.83	$5.85	$5.80
Purchase #3	$140.99	7.334%	$151.3302	$151.33	$151.35	$151.30
Purchase #4	$238.95	8.757%	$259.8749	$259.87	$259.85	$259.90
Purchase #5	$85.70	3.538%	$88.7321	$88.73	$88.75	$88.70
Purchase #6	$45.98	8.232%	$49.7651	$49.77	$49.75	$49.80
Purchase #7	$88.26	4.383%	$92.1284	$92.13	$92.15	$92.10
7 purchase totals =	$705.88		$758.9835	$758.98	$759.00	$758.90