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	$50.51	10.492%	$55.8095	$55.81	$55.80	$55.80
Purchase #2	$114.64	10.825%	$127.0498	$127.05	$127.05	$127.00
Purchase #3	$53.49	12.636%	$60.249	$60.25	$60.25	$60.20
Purchase #4	$84.40	6.191%	$89.6252	$89.63	$89.65	$89.60
Purchase #5	$234.53	9.490%	$256.7869	$256.79	$256.80	$256.80
Purchase #6	$209.76	9.279%	$229.2236	$229.22	$229.20	$229.20
Purchase #7	$155.94	4.228%	$162.5331	$162.53	$162.55	$162.50
7 purchase totals =	$903.27		$981.2771	$981.28	$981.30	$981.10