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	$210.70	8.428%	$228.4578	$228.46	$228.45	$228.50
Purchase #2	$154.26	7.228%	$165.4099	$165.41	$165.40	$165.40
Purchase #3	$70.90	11.810%	$79.2733	$79.27	$79.25	$79.30
Purchase #4	$202.41	9.841%	$222.3292	$222.33	$222.35	$222.30
Purchase #5	$166.89	3.384%	$172.5376	$172.54	$172.55	$172.50
Purchase #6	$29.34	12.329%	$32.9573	$32.96	$32.95	$33.00
Purchase #7	$53.41	10.714%	$59.1323	$59.13	$59.15	$59.10
7 purchase totals =	$887.91		$960.0974	$960.10	$960.10	$960.10