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	$61.56	8.251%	$66.6393	$66.64	$66.65	$66.60
Purchase #2	$177.71	4.593%	$185.8722	$185.87	$185.85	$185.90
Purchase #3	$167.50	10.552%	$185.1746	$185.17	$185.15	$185.20
Purchase #4	$19.75	4.797%	$20.6974	$20.70	$20.70	$20.70
Purchase #5	$98.35	5.170%	$103.4347	$103.43	$103.45	$103.40
Purchase #6	$104.62	12.347%	$117.5374	$117.54	$117.55	$117.50
Purchase #7	$55.30	6.503%	$58.8962	$58.90	$58.90	$58.90
7 purchase totals =	$684.79		$738.2518	$738.25	$738.25	$738.20