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	$115.47	13.570%	$131.1393	$131.14	$131.15	$131.10
Purchase #2	$86.57	3.337%	$89.4588	$89.46	$89.45	$89.50
Purchase #3	$15.81	6.666%	$16.8639	$16.86	$16.85	$16.90
Purchase #4	$60.92	3.363%	$62.9687	$62.97	$62.95	$63.00
Purchase #5	$17.75	4.572%	$18.5615	$18.56	$18.55	$18.60
Purchase #6	$137.79	8.342%	$149.2844	$149.28	$149.30	$149.30
Purchase #7	$35.64	9.714%	$39.1021	$39.10	$39.10	$39.10
7 purchase totals =	$469.95		$507.3787	$507.37	$507.35	$507.50