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	$139.59	7.327%	$149.8178	$149.82	$149.80	$149.80
Purchase #2	$214.44	8.324%	$232.29	$232.29	$232.30	$232.30
Purchase #3	$134.79	9.554%	$147.6678	$147.67	$147.65	$147.70
Purchase #4	$190.54	11.568%	$212.5817	$212.58	$212.60	$212.60
Purchase #5	$53.32	11.751%	$59.5856	$59.59	$59.60	$59.60
Purchase #6	$161.87	6.557%	$172.4838	$172.48	$172.50	$172.50
Purchase #7	$25.43	10.157%	$28.0129	$28.01	$28.00	$28.00
7 purchase totals =	$919.98		$1,002.4396	$1,002.44	$1,002.45	$1,002.50