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	$229.48	6.121%	$243.5265	$243.53	$243.55	$243.50
Purchase #2	$33.64	11.340%	$37.4548	$37.45	$37.45	$37.50
Purchase #3	$69.89	13.777%	$79.5187	$79.52	$79.50	$79.50
Purchase #4	$12.30	13.104%	$13.9118	$13.91	$13.90	$13.90
Purchase #5	$12.44	11.734%	$13.8997	$13.90	$13.90	$13.90
Purchase #6	$144.74	10.573%	$160.0434	$160.04	$160.05	$160.00
Purchase #7	$123.89	4.754%	$129.7797	$129.78	$129.80	$129.80
7 purchase totals =	$626.38		$678.1346	$678.13	$678.15	$678.10