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	$42.57	6.221%	$45.2183	$45.22	$45.20	$45.20
Purchase #2	$35.80	9.489%	$39.1971	$39.20	$39.20	$39.20
Purchase #3	$74.59	10.563%	$82.4689	$82.47	$82.45	$82.50
Purchase #4	$84.53	3.592%	$87.5663	$87.57	$87.55	$87.60
Purchase #5	$47.83	10.239%	$52.7273	$52.73	$52.75	$52.70
Purchase #6	$137.27	12.766%	$154.7939	$154.79	$154.80	$154.80
Purchase #7	$149.89	10.182%	$165.1518	$165.15	$165.15	$165.20
7 purchase totals =	$572.48		$627.1236	$627.13	$627.10	$627.20