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	$143.44	7.430%	$154.0976	$154.10	$154.10	$154.10
Purchase #2	$185.50	11.181%	$206.2408	$206.24	$206.25	$206.20
Purchase #3	$122.90	7.342%	$131.9233	$131.92	$131.90	$131.90
Purchase #4	$145.51	10.377%	$160.6096	$160.61	$160.60	$160.60
Purchase #5	$99.61	4.147%	$103.7408	$103.74	$103.75	$103.70
Purchase #6	$129.45	6.244%	$137.5329	$137.53	$137.55	$137.50
Purchase #7	$91.89	4.847%	$96.3439	$96.34	$96.35	$96.30
7 purchase totals =	$918.30		$990.4889	$990.48	$990.50	$990.30