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	$240.26	6.232%	$255.233	$255.23	$255.25	$255.20
Purchase #2	$104.26	10.145%	$114.8372	$114.84	$114.85	$114.80
Purchase #3	$32.96	13.494%	$37.4076	$37.41	$37.40	$37.40
Purchase #4	$239.38	10.519%	$264.5604	$264.56	$264.55	$264.60
Purchase #5	$235.91	6.228%	$250.6025	$250.60	$250.60	$250.60
Purchase #6	$220.85	11.582%	$246.4288	$246.43	$246.45	$246.40
Purchase #7	$137.31	12.110%	$153.9382	$153.94	$153.95	$153.90
7 purchase totals =	$1,210.93		$1,323.0077	$1,323.01	$1,323.05	$1,322.90