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	$222.30	4.137%	$231.4966	$231.50	$231.50	$231.50
Purchase #2	$108.44	11.113%	$120.4909	$120.49	$120.50	$120.50
Purchase #3	$80.73	10.601%	$89.2882	$89.29	$89.30	$89.30
Purchase #4	$94.98	10.294%	$104.7572	$104.76	$104.75	$104.80
Purchase #5	$242.45	3.595%	$251.1661	$251.17	$251.15	$251.20
Purchase #6	$225.87	13.183%	$255.6464	$255.65	$255.65	$255.60
Purchase #7	$7.51	12.511%	$8.4496	$8.45	$8.45	$8.40
7 purchase totals =	$982.28		$1,061.2950	$1,061.31	$1,061.30	$1,061.30