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	$165.52	6.156%	$175.7094	$175.71	$175.70	$175.70
Purchase #2	$28.85	10.159%	$31.7809	$31.78	$31.80	$31.80
Purchase #3	$99.27	12.741%	$111.918	$111.92	$111.90	$111.90
Purchase #4	$244.94	12.585%	$275.7657	$275.77	$275.75	$275.80
Purchase #5	$164.33	3.213%	$169.6099	$169.61	$169.60	$169.60
Purchase #6	$160.70	3.201%	$165.844	$165.84	$165.85	$165.80
Purchase #7	$57.33	9.349%	$62.6898	$62.69	$62.70	$62.70
7 purchase totals =	$920.94		$993.3177	$993.32	$993.30	$993.30