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	$77.93	4.215%	$81.2147	$81.21	$81.20	$81.20
Purchase #2	$46.74	10.133%	$51.4762	$51.48	$51.50	$51.50
Purchase #3	$81.31	10.353%	$89.728	$89.73	$89.75	$89.70
Purchase #4	$46.51	9.399%	$50.8815	$50.88	$50.90	$50.90
Purchase #5	$70.68	4.625%	$73.949	$73.95	$73.95	$73.90
Purchase #6	$139.62	11.437%	$155.5883	$155.59	$155.60	$155.60
Purchase #7	$143.92	11.473%	$160.4319	$160.43	$160.45	$160.40
7 purchase totals =	$606.71		$663.2696	$663.27	$663.35	$663.20