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	$103.78	13.714%	$118.0124	$118.01	$118.00	$118.00
Purchase #2	$51.47	9.158%	$56.1836	$56.18	$56.20	$56.20
Purchase #3	$156.34	9.410%	$171.0516	$171.05	$171.05	$171.10
Purchase #4	$110.49	6.515%	$117.6884	$117.69	$117.70	$117.70
Purchase #5	$134.71	4.854%	$141.2488	$141.25	$141.25	$141.20
Purchase #6	$152.99	8.194%	$165.526	$165.53	$165.55	$165.50
Purchase #7	$173.40	9.673%	$190.173	$190.17	$190.15	$190.20
7 purchase totals =	$883.18		$959.8838	$959.88	$959.90	$959.90