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	$124.28	5.227%	$130.7761	$130.78	$130.80	$130.80
Purchase #2	$14.88	4.802%	$15.5945	$15.59	$15.60	$15.60
Purchase #3	$237.88	13.195%	$269.2683	$269.27	$269.25	$269.30
Purchase #4	$226.56	10.293%	$249.8798	$249.88	$249.90	$249.90
Purchase #5	$174.80	12.754%	$197.094	$197.09	$197.10	$197.10
Purchase #6	$210.61	6.339%	$223.9606	$223.96	$223.95	$224.00
Purchase #7	$35.88	3.547%	$37.1527	$37.15	$37.15	$37.20
7 purchase totals =	$1,024.89		$1,123.7260	$1,123.72	$1,123.75	$1,123.90