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	$233.61	8.439%	$253.3243	$253.32	$253.30	$253.30
Purchase #2	$37.64	7.125%	$40.3219	$40.32	$40.30	$40.30
Purchase #3	$215.64	4.414%	$225.1583	$225.16	$225.15	$225.20
Purchase #4	$230.58	10.768%	$255.4089	$255.41	$255.40	$255.40
Purchase #5	$124.58	11.845%	$139.3365	$139.34	$139.35	$139.30
Purchase #6	$199.41	5.444%	$210.2659	$210.27	$210.25	$210.30
Purchase #7	$168.31	4.360%	$175.6483	$175.65	$175.65	$175.60
7 purchase totals =	$1,209.77		$1,299.4641	$1,299.47	$1,299.40	$1,299.40