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	$190.75	11.541%	$212.7645	$212.76	$212.75	$212.80
Purchase #2	$12.25	10.163%	$13.495	$13.50	$13.50	$13.50
Purchase #3	$170.77	13.705%	$194.174	$194.17	$194.15	$194.20
Purchase #4	$18.80	11.213%	$20.908	$20.91	$20.90	$20.90
Purchase #5	$212.71	5.175%	$223.7177	$223.72	$223.70	$223.70
Purchase #6	$10.72	10.285%	$11.8226	$11.82	$11.80	$11.80
Purchase #7	$31.26	3.716%	$32.4216	$32.42	$32.40	$32.40
7 purchase totals =	$647.26		$709.3034	$709.30	$709.20	$709.30