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	$85.74	4.726%	$89.7921	$89.79	$89.80	$89.80
Purchase #2	$53.53	8.367%	$58.0089	$58.01	$58.00	$58.00
Purchase #3	$182.57	9.194%	$199.3555	$199.36	$199.35	$199.40
Purchase #4	$190.34	13.513%	$216.0606	$216.06	$216.05	$216.10
Purchase #5	$33.49	13.838%	$38.1243	$38.12	$38.10	$38.10
Purchase #6	$227.57	6.342%	$242.0025	$242.00	$242.00	$242.00
Purchase #7	$228.64	4.224%	$238.2978	$238.30	$238.30	$238.30
7 purchase totals =	$1,001.88		$1,081.6417	$1,081.64	$1,081.60	$1,081.70