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	$10.83	10.187%	$11.9333	$11.93	$11.95	$11.90
Purchase #2	$136.36	4.257%	$142.1648	$142.16	$142.15	$142.20
Purchase #3	$111.93	7.555%	$120.3863	$120.39	$120.40	$120.40
Purchase #4	$100.58	11.158%	$111.8027	$111.80	$111.80	$111.80
Purchase #5	$203.84	9.662%	$223.535	$223.54	$223.55	$223.50
Purchase #6	$152.82	3.855%	$158.7112	$158.71	$158.70	$158.70
Purchase #7	$178.50	6.275%	$189.7009	$189.70	$189.70	$189.70
7 purchase totals =	$894.86		$958.2342	$958.23	$958.25	$958.20