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	$220.90	5.693%	$233.4758	$233.48	$233.50	$233.50
Purchase #2	$138.73	11.344%	$154.4675	$154.47	$154.45	$154.50
Purchase #3	$144.92	7.123%	$155.2427	$155.24	$155.25	$155.20
Purchase #4	$125.89	10.779%	$139.4597	$139.46	$139.45	$139.50
Purchase #5	$71.33	11.404%	$79.4645	$79.46	$79.45	$79.50
Purchase #6	$68.25	6.232%	$72.5033	$72.50	$72.50	$72.50
Purchase #7	$99.62	6.464%	$106.0594	$106.06	$106.05	$106.10
7 purchase totals =	$869.64		$940.6729	$940.67	$940.65	$940.80