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	$50.91	12.123%	$57.0818	$57.08	$57.10	$57.10
Purchase #2	$242.50	4.385%	$253.1336	$253.13	$253.15	$253.10
Purchase #3	$38.39	10.721%	$42.5058	$42.51	$42.50	$42.50
Purchase #4	$61.36	10.197%	$67.6169	$67.62	$67.60	$67.60
Purchase #5	$224.44	13.627%	$255.0244	$255.02	$255.00	$255.00
Purchase #6	$190.58	11.146%	$211.822	$211.82	$211.80	$211.80
Purchase #7	$72.33	9.840%	$79.4473	$79.45	$79.45	$79.40
7 purchase totals =	$880.51		$966.6318	$966.63	$966.60	$966.50