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	$72.65	10.599%	$80.3502	$80.35	$80.35	$80.40
Purchase #2	$67.73	7.645%	$72.908	$72.91	$72.90	$72.90
Purchase #3	$84.53	7.137%	$90.5629	$90.56	$90.55	$90.60
Purchase #4	$222.75	10.222%	$245.5195	$245.52	$245.50	$245.50
Purchase #5	$137.41	6.797%	$146.7498	$146.75	$146.75	$146.70
Purchase #6	$15.47	10.472%	$17.09	$17.09	$17.10	$17.10
Purchase #7	$79.82	12.710%	$89.9651	$89.97	$89.95	$90.00
7 purchase totals =	$680.36		$743.1455	$743.15	$743.10	$743.20