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	$149.27	11.692%	$166.7226	$166.72	$166.70	$166.70
Purchase #2	$145.98	8.463%	$158.3343	$158.33	$158.35	$158.30
Purchase #3	$116.68	12.361%	$131.1028	$131.10	$131.10	$131.10
Purchase #4	$56.65	9.338%	$61.94	$61.94	$61.95	$61.90
Purchase #5	$82.95	13.172%	$93.8762	$93.88	$93.90	$93.90
Purchase #6	$235.64	6.437%	$250.8081	$250.81	$250.80	$250.80
Purchase #7	$104.33	4.812%	$109.3504	$109.35	$109.35	$109.40
7 purchase totals =	$891.50		$972.1344	$972.13	$972.15	$972.10