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	$223.41	13.303%	$253.1302	$253.13	$253.15	$253.10
Purchase #2	$133.97	13.280%	$151.7612	$151.76	$151.75	$151.80
Purchase #3	$35.45	5.503%	$37.4008	$37.40	$37.40	$37.40
Purchase #4	$140.81	5.328%	$148.3124	$148.31	$148.30	$148.30
Purchase #5	$150.57	5.473%	$158.8107	$158.81	$158.80	$158.80
Purchase #6	$12.61	10.211%	$13.8976	$13.90	$13.90	$13.90
Purchase #7	$102.49	12.389%	$115.1875	$115.19	$115.20	$115.20
7 purchase totals =	$799.31		$878.5004	$878.50	$878.50	$878.50