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	$139.63	7.802%	$150.5239	$150.52	$150.50	$150.50
Purchase #2	$96.37	12.728%	$108.636	$108.64	$108.65	$108.60
Purchase #3	$201.88	3.461%	$208.8671	$208.87	$208.85	$208.90
Purchase #4	$250.85	10.840%	$278.0421	$278.04	$278.05	$278.00
Purchase #5	$26.89	13.483%	$30.5156	$30.52	$30.50	$30.50
Purchase #6	$89.63	11.127%	$99.6031	$99.60	$99.60	$99.60
Purchase #7	$32.29	5.487%	$34.0618	$34.06	$34.05	$34.10
7 purchase totals =	$837.54		$910.2496	$910.25	$910.20	$910.20