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	$123.56	4.209%	$128.7606	$128.76	$128.75	$128.80
Purchase #2	$117.84	11.822%	$131.771	$131.77	$131.75	$131.80
Purchase #3	$146.59	9.115%	$159.9517	$159.95	$159.95	$160.00
Purchase #4	$45.49	5.323%	$47.9114	$47.91	$47.90	$47.90
Purchase #5	$188.43	4.150%	$196.2498	$196.25	$196.25	$196.20
Purchase #6	$29.95	5.795%	$31.6856	$31.69	$31.70	$31.70
Purchase #7	$118.42	10.860%	$131.2804	$131.28	$131.30	$131.30
7 purchase totals =	$770.28		$827.6105	$827.61	$827.60	$827.70