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	$154.40	12.156%	$173.1689	$173.17	$173.15	$173.20
Purchase #2	$138.54	3.119%	$142.8611	$142.86	$142.85	$142.90
Purchase #3	$114.59	12.499%	$128.9126	$128.91	$128.90	$128.90
Purchase #4	$155.75	10.741%	$172.4791	$172.48	$172.50	$172.50
Purchase #5	$161.45	8.584%	$175.3089	$175.31	$175.30	$175.30
Purchase #6	$5.48	13.306%	$6.2092	$6.21	$6.20	$6.20
Purchase #7	$190.97	13.327%	$216.4206	$216.42	$216.40	$216.40
7 purchase totals =	$921.18		$1,015.3604	$1,015.36	$1,015.30	$1,015.40