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	$136.41	7.361%	$146.4511	$146.45	$146.45	$146.50
Purchase #2	$53.44	13.820%	$60.8254	$60.83	$60.85	$60.80
Purchase #3	$226.87	9.245%	$247.8441	$247.84	$247.85	$247.80
Purchase #4	$24.52	10.827%	$27.1748	$27.17	$27.15	$27.20
Purchase #5	$182.90	4.297%	$190.7592	$190.76	$190.75	$190.80
Purchase #6	$162.61	5.393%	$171.3796	$171.38	$171.40	$171.40
Purchase #7	$164.97	6.555%	$175.7838	$175.78	$175.80	$175.80
7 purchase totals =	$951.72		$1,020.2180	$1,020.21	$1,020.25	$1,020.30