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	$234.93	10.339%	$259.2194	$259.22	$259.20	$259.20
Purchase #2	$130.57	8.828%	$142.0967	$142.10	$142.10	$142.10
Purchase #3	$220.68	13.405%	$250.2622	$250.26	$250.25	$250.30
Purchase #4	$87.85	13.718%	$99.9013	$99.90	$99.90	$99.90
Purchase #5	$106.86	4.232%	$111.3823	$111.38	$111.40	$111.40
Purchase #6	$137.72	6.250%	$146.3275	$146.33	$146.35	$146.30
Purchase #7	$13.62	6.679%	$14.5297	$14.53	$14.55	$14.50
7 purchase totals =	$932.23		$1,023.7191	$1,023.72	$1,023.75	$1,023.70