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	$103.78	11.559%	$115.7759	$115.78	$115.80	$115.80
Purchase #2	$66.47	9.516%	$72.7953	$72.80	$72.80	$72.80
Purchase #3	$148.33	13.371%	$168.1632	$168.16	$168.15	$168.20
Purchase #4	$38.38	10.428%	$42.3823	$42.38	$42.40	$42.40
Purchase #5	$146.28	5.237%	$153.9407	$153.94	$153.95	$153.90
Purchase #6	$230.85	8.325%	$250.0683	$250.07	$250.05	$250.10
Purchase #7	$162.41	10.777%	$179.9129	$179.91	$179.90	$179.90
7 purchase totals =	$896.50		$983.0386	$983.04	$983.05	$983.10