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	$18.86	13.707%	$21.4451	$21.45	$21.45	$21.40
Purchase #2	$65.45	3.728%	$67.89	$67.89	$67.90	$67.90
Purchase #3	$88.89	3.373%	$91.8883	$91.89	$91.90	$91.90
Purchase #4	$245.89	8.230%	$266.1267	$266.13	$266.15	$266.10
Purchase #5	$80.30	3.322%	$82.9676	$82.97	$82.95	$83.00
Purchase #6	$149.63	3.495%	$154.8596	$154.86	$154.85	$154.90
Purchase #7	$171.73	3.332%	$177.452	$177.45	$177.45	$177.50
7 purchase totals =	$820.75		$862.6293	$862.64	$862.65	$862.70