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	$62.91	11.370%	$70.0629	$70.06	$70.05	$70.10
Purchase #2	$152.56	13.600%	$173.3082	$173.31	$173.30	$173.30
Purchase #3	$212.92	4.556%	$222.6206	$222.62	$222.60	$222.60
Purchase #4	$150.63	9.198%	$164.4849	$164.48	$164.50	$164.50
Purchase #5	$217.77	13.472%	$247.108	$247.11	$247.10	$247.10
Purchase #6	$248.90	10.181%	$274.2405	$274.24	$274.25	$274.20
Purchase #7	$249.81	7.707%	$269.0629	$269.06	$269.05	$269.10
7 purchase totals =	$1,295.50		$1,420.8880	$1,420.88	$1,420.85	$1,420.90