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	$39.28	5.873%	$41.5869	$41.59	$41.60	$41.60
Purchase #2	$190.41	4.642%	$199.2488	$199.25	$199.25	$199.20
Purchase #3	$164.67	13.763%	$187.3335	$187.33	$187.35	$187.30
Purchase #4	$209.94	8.656%	$228.1124	$228.11	$228.10	$228.10
Purchase #5	$92.78	11.171%	$103.1445	$103.14	$103.15	$103.10
Purchase #6	$149.37	6.279%	$158.7489	$158.75	$158.75	$158.70
Purchase #7	$31.45	4.707%	$32.9304	$32.93	$32.95	$32.90
7 purchase totals =	$877.90		$951.1054	$951.10	$951.15	$950.90