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	$91.52	9.580%	$100.2876	$100.29	$100.30	$100.30
Purchase #2	$185.85	11.297%	$206.8455	$206.85	$206.85	$206.80
Purchase #3	$37.27	5.366%	$39.2699	$39.27	$39.25	$39.30
Purchase #4	$103.85	5.640%	$109.7071	$109.71	$109.70	$109.70
Purchase #5	$134.53	12.871%	$151.8454	$151.85	$151.85	$151.80
Purchase #6	$77.93	13.369%	$88.3485	$88.35	$88.35	$88.30
Purchase #7	$164.74	11.598%	$183.8465	$183.85	$183.85	$183.80
7 purchase totals =	$795.69		$880.1505	$880.17	$880.15	$880.00