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	$19.98	12.670%	$22.5115	$22.51	$22.50	$22.50
Purchase #2	$103.56	5.707%	$109.4702	$109.47	$109.45	$109.50
Purchase #3	$135.32	10.472%	$149.4907	$149.49	$149.50	$149.50
Purchase #4	$44.34	7.549%	$47.6872	$47.69	$47.70	$47.70
Purchase #5	$54.99	12.502%	$61.8648	$61.86	$61.85	$61.90
Purchase #6	$123.45	4.282%	$128.7361	$128.74	$128.75	$128.70
Purchase #7	$245.53	9.599%	$269.0984	$269.10	$269.10	$269.10
7 purchase totals =	$727.17		$788.8589	$788.86	$788.85	$788.90