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	$66.91	6.498%	$71.2578	$71.26	$71.25	$71.30
Purchase #2	$170.69	12.261%	$191.6183	$191.62	$191.60	$191.60
Purchase #3	$100.27	5.447%	$105.7317	$105.73	$105.75	$105.70
Purchase #4	$59.55	13.859%	$67.803	$67.80	$67.80	$67.80
Purchase #5	$227.39	13.348%	$257.742	$257.74	$257.75	$257.70
Purchase #6	$28.34	10.250%	$31.2449	$31.24	$31.25	$31.20
Purchase #7	$34.83	9.575%	$38.165	$38.17	$38.15	$38.20
7 purchase totals =	$687.98		$763.5627	$763.56	$763.55	$763.50