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	$127.52	11.787%	$142.5508	$142.55	$142.55	$142.60
Purchase #2	$54.77	8.754%	$59.5646	$59.56	$59.55	$59.60
Purchase #3	$17.69	9.642%	$19.3957	$19.40	$19.40	$19.40
Purchase #4	$36.69	7.401%	$39.4054	$39.41	$39.40	$39.40
Purchase #5	$174.91	13.295%	$198.1643	$198.16	$198.15	$198.20
Purchase #6	$150.39	6.111%	$159.5803	$159.58	$159.60	$159.60
Purchase #7	$177.86	7.640%	$191.4485	$191.45	$191.45	$191.40
7 purchase totals =	$739.83		$810.1096	$810.11	$810.10	$810.20