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	$220.94	9.153%	$241.1626	$241.16	$241.15	$241.20
Purchase #2	$65.65	7.427%	$70.5258	$70.53	$70.55	$70.50
Purchase #3	$71.79	9.632%	$78.7048	$78.70	$78.70	$78.70
Purchase #4	$39.55	9.740%	$43.4022	$43.40	$43.40	$43.40
Purchase #5	$223.35	3.745%	$231.7145	$231.71	$231.70	$231.70
Purchase #6	$156.54	7.205%	$167.8187	$167.82	$167.80	$167.80
Purchase #7	$127.52	13.380%	$144.5822	$144.58	$144.60	$144.60
7 purchase totals =	$905.34		$977.9108	$977.90	$977.90	$977.90