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	$173.92	3.261%	$179.5915	$179.59	$179.60	$179.60
Purchase #2	$221.28	13.811%	$251.841	$251.84	$251.85	$251.80
Purchase #3	$106.59	4.646%	$111.5422	$111.54	$111.55	$111.50
Purchase #4	$206.30	3.375%	$213.2626	$213.26	$213.25	$213.30
Purchase #5	$79.93	7.638%	$86.0351	$86.04	$86.05	$86.00
Purchase #6	$27.70	4.139%	$28.8465	$28.85	$28.85	$28.80
Purchase #7	$86.82	13.306%	$98.3723	$98.37	$98.35	$98.40
7 purchase totals =	$902.54		$969.4912	$969.49	$969.50	$969.40