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	$45.89	13.794%	$52.2201	$52.22	$52.20	$52.20
Purchase #2	$14.50	3.367%	$14.9882	$14.99	$15.00	$15.00
Purchase #3	$89.62	13.142%	$101.3979	$101.40	$101.40	$101.40
Purchase #4	$154.81	3.445%	$160.1432	$160.14	$160.15	$160.10
Purchase #5	$52.52	3.345%	$54.2768	$54.28	$54.30	$54.30
Purchase #6	$38.34	9.497%	$41.9811	$41.98	$42.00	$42.00
Purchase #7	$23.84	13.853%	$27.1426	$27.14	$27.15	$27.10
7 purchase totals =	$419.52		$452.1499	$452.15	$452.20	$452.10