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	$80.47	12.194%	$90.2825	$90.28	$90.30	$90.30
Purchase #2	$140.37	13.622%	$159.4912	$159.49	$159.50	$159.50
Purchase #3	$78.70	12.297%	$88.3777	$88.38	$88.40	$88.40
Purchase #4	$54.29	11.668%	$60.6246	$60.62	$60.60	$60.60
Purchase #5	$200.49	11.639%	$223.825	$223.83	$223.85	$223.80
Purchase #6	$25.78	7.820%	$27.796	$27.80	$27.80	$27.80
Purchase #7	$224.90	8.310%	$243.5892	$243.59	$243.60	$243.60
7 purchase totals =	$805.00		$893.9862	$893.99	$894.05	$894.00