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	$81.65	9.401%	$89.3259	$89.33	$89.35	$89.30
Purchase #2	$49.51	5.326%	$52.1469	$52.15	$52.15	$52.10
Purchase #3	$158.34	7.523%	$170.2519	$170.25	$170.25	$170.30
Purchase #4	$195.71	8.350%	$212.0518	$212.05	$212.05	$212.10
Purchase #5	$40.59	4.618%	$42.4644	$42.46	$42.45	$42.50
Purchase #6	$149.95	8.563%	$162.7902	$162.79	$162.80	$162.80
Purchase #7	$137.66	13.464%	$156.1945	$156.19	$156.20	$156.20
7 purchase totals =	$813.41		$885.2256	$885.22	$885.25	$885.30