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	$206.51	9.328%	$225.7733	$225.77	$225.75	$225.80
Purchase #2	$105.88	9.729%	$116.1811	$116.18	$116.20	$116.20
Purchase #3	$106.87	12.771%	$120.5184	$120.52	$120.50	$120.50
Purchase #4	$70.30	11.852%	$78.632	$78.63	$78.65	$78.60
Purchase #5	$167.66	4.588%	$175.3522	$175.35	$175.35	$175.40
Purchase #6	$77.27	6.152%	$82.0237	$82.02	$82.00	$82.00
Purchase #7	$102.35	8.435%	$110.9832	$110.98	$111.00	$111.00
7 purchase totals =	$836.84		$909.4639	$909.45	$909.45	$909.50