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	$111.52	10.579%	$123.3177	$123.32	$123.30	$123.30
Purchase #2	$196.77	8.188%	$212.8815	$212.88	$212.90	$212.90
Purchase #3	$79.33	5.550%	$83.7328	$83.73	$83.75	$83.70
Purchase #4	$175.86	11.436%	$195.9713	$195.97	$195.95	$196.00
Purchase #5	$230.48	3.634%	$238.8556	$238.86	$238.85	$238.90
Purchase #6	$201.90	12.150%	$226.4309	$226.43	$226.45	$226.40
Purchase #7	$199.33	11.414%	$222.0815	$222.08	$222.10	$222.10
7 purchase totals =	$1,195.19		$1,303.2713	$1,303.27	$1,303.30	$1,303.30