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	$16.71	8.627%	$18.1516	$18.15	$18.15	$18.20
Purchase #2	$101.49	8.367%	$109.9817	$109.98	$110.00	$110.00
Purchase #3	$45.78	7.525%	$49.2249	$49.22	$49.20	$49.20
Purchase #4	$122.41	7.235%	$131.2664	$131.27	$131.25	$131.30
Purchase #5	$101.65	3.209%	$104.9119	$104.91	$104.90	$104.90
Purchase #6	$79.51	12.517%	$89.4623	$89.46	$89.45	$89.50
Purchase #7	$80.63	6.379%	$85.7734	$85.77	$85.75	$85.80
7 purchase totals =	$548.18		$588.7722	$588.76	$588.70	$588.90