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	$204.40	13.449%	$231.8898	$231.89	$231.90	$231.90
Purchase #2	$36.30	9.552%	$39.7674	$39.77	$39.75	$39.80
Purchase #3	$91.44	6.691%	$97.5583	$97.56	$97.55	$97.60
Purchase #4	$190.61	11.493%	$212.5168	$212.52	$212.50	$212.50
Purchase #5	$200.28	12.692%	$225.6995	$225.70	$225.70	$225.70
Purchase #6	$64.57	10.319%	$71.233	$71.23	$71.25	$71.20
Purchase #7	$100.55	3.663%	$104.2331	$104.23	$104.25	$104.20
7 purchase totals =	$888.15		$982.8979	$982.90	$982.90	$982.90