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	$229.52	6.209%	$243.7709	$243.77	$243.75	$243.80
Purchase #2	$130.85	5.779%	$138.4118	$138.41	$138.40	$138.40
Purchase #3	$90.70	10.815%	$100.5092	$100.51	$100.50	$100.50
Purchase #4	$138.81	4.485%	$145.0356	$145.04	$145.05	$145.00
Purchase #5	$93.34	8.731%	$101.4895	$101.49	$101.50	$101.50
Purchase #6	$7.97	7.595%	$8.5753	$8.58	$8.60	$8.60
Purchase #7	$233.33	9.430%	$255.333	$255.33	$255.35	$255.30
7 purchase totals =	$924.52		$993.1253	$993.13	$993.15	$993.10