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	$154.85	8.117%	$167.4192	$167.42	$167.40	$167.40
Purchase #2	$223.71	13.124%	$253.0697	$253.07	$253.05	$253.10
Purchase #3	$178.25	7.807%	$192.166	$192.17	$192.15	$192.20
Purchase #4	$156.70	3.618%	$162.3694	$162.37	$162.35	$162.40
Purchase #5	$69.60	13.140%	$78.7454	$78.75	$78.75	$78.70
Purchase #6	$250.45	5.648%	$264.5954	$264.60	$264.60	$264.60
Purchase #7	$55.40	11.402%	$61.7167	$61.72	$61.70	$61.70
7 purchase totals =	$1,088.96		$1,180.0818	$1,180.10	$1,180.00	$1,180.10