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	$78.62	13.511%	$89.2423	$89.24	$89.25	$89.20
Purchase #2	$205.76	11.176%	$228.7557	$228.76	$228.75	$228.80
Purchase #3	$48.95	13.150%	$55.3869	$55.39	$55.40	$55.40
Purchase #4	$116.27	6.503%	$123.831	$123.83	$123.85	$123.80
Purchase #5	$152.58	4.576%	$159.5621	$159.56	$159.55	$159.60
Purchase #6	$60.76	4.531%	$63.513	$63.51	$63.50	$63.50
Purchase #7	$228.63	4.166%	$238.1547	$238.15	$238.15	$238.20
7 purchase totals =	$891.57		$958.4457	$958.44	$958.45	$958.50