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	$185.54	11.364%	$206.6248	$206.62	$206.60	$206.60
Purchase #2	$75.36	12.322%	$84.6459	$84.65	$84.65	$84.60
Purchase #3	$10.43	8.162%	$11.2813	$11.28	$11.30	$11.30
Purchase #4	$80.69	10.534%	$89.1899	$89.19	$89.20	$89.20
Purchase #5	$111.61	10.266%	$123.0679	$123.07	$123.05	$123.10
Purchase #6	$71.87	8.846%	$78.2276	$78.23	$78.25	$78.20
Purchase #7	$174.94	3.298%	$180.7095	$180.71	$180.70	$180.70
7 purchase totals =	$710.44		$773.7469	$773.75	$773.75	$773.70