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	$93.50	12.667%	$105.3436	$105.34	$105.35	$105.30
Purchase #2	$33.83	13.598%	$38.4302	$38.43	$38.45	$38.40
Purchase #3	$20.74	5.213%	$21.8212	$21.82	$21.80	$21.80
Purchase #4	$222.30	10.231%	$245.0435	$245.04	$245.05	$245.00
Purchase #5	$191.84	4.423%	$200.3251	$200.33	$200.35	$200.30
Purchase #6	$66.32	11.244%	$73.777	$73.78	$73.80	$73.80
Purchase #7	$80.32	6.351%	$85.4211	$85.42	$85.40	$85.40
7 purchase totals =	$708.85		$770.1617	$770.16	$770.20	$770.00