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	$183.74	3.705%	$190.5476	$190.55	$190.55	$190.50
Purchase #2	$244.61	9.671%	$268.2662	$268.27	$268.25	$268.30
Purchase #3	$31.91	5.346%	$33.6159	$33.62	$33.60	$33.60
Purchase #4	$39.49	12.855%	$44.5664	$44.57	$44.55	$44.60
Purchase #5	$178.36	4.164%	$185.7869	$185.79	$185.80	$185.80
Purchase #6	$9.31	10.501%	$10.2876	$10.29	$10.30	$10.30
Purchase #7	$34.73	6.844%	$37.1069	$37.11	$37.10	$37.10
7 purchase totals =	$722.15		$770.1775	$770.20	$770.15	$770.20