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	$106.92	10.456%	$118.0996	$118.10	$118.10	$118.10
Purchase #2	$244.62	12.771%	$275.8604	$275.86	$275.85	$275.90
Purchase #3	$33.97	11.206%	$37.7767	$37.78	$37.80	$37.80
Purchase #4	$45.75	6.565%	$48.7535	$48.75	$48.75	$48.80
Purchase #5	$53.70	3.301%	$55.4726	$55.47	$55.45	$55.50
Purchase #6	$84.85	5.766%	$89.7425	$89.74	$89.75	$89.70
Purchase #7	$79.38	10.735%	$87.9014	$87.90	$87.90	$87.90
7 purchase totals =	$649.19		$713.6067	$713.60	$713.60	$713.70