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	$164.84	4.824%	$172.7919	$172.79	$172.80	$172.80
Purchase #2	$90.65	4.338%	$94.5824	$94.58	$94.60	$94.60
Purchase #3	$92.30	9.829%	$101.3722	$101.37	$101.35	$101.40
Purchase #4	$149.28	6.107%	$158.3965	$158.40	$158.40	$158.40
Purchase #5	$78.90	11.822%	$88.2276	$88.23	$88.25	$88.20
Purchase #6	$137.54	7.214%	$147.4621	$147.46	$147.45	$147.50
Purchase #7	$222.55	9.217%	$243.0624	$243.06	$243.05	$243.10
7 purchase totals =	$936.06		$1,005.8951	$1,005.89	$1,005.90	$1,006.00