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	$78.54	12.560%	$88.4046	$88.40	$88.40	$88.40
Purchase #2	$153.58	7.820%	$165.59	$165.59	$165.60	$165.60
Purchase #3	$126.34	4.292%	$131.7625	$131.76	$131.75	$131.80
Purchase #4	$52.59	8.612%	$57.1191	$57.12	$57.10	$57.10
Purchase #5	$120.77	5.528%	$127.4462	$127.45	$127.45	$127.40
Purchase #6	$202.30	4.243%	$210.8836	$210.88	$210.90	$210.90
Purchase #7	$22.72	7.369%	$24.3942	$24.39	$24.40	$24.40
7 purchase totals =	$756.84		$805.6002	$805.59	$805.60	$805.60