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	$73.60	6.545%	$78.4171	$78.42	$78.40	$78.40
Purchase #2	$108.57	11.330%	$120.871	$120.87	$120.85	$120.90
Purchase #3	$26.74	6.398%	$28.4508	$28.45	$28.45	$28.50
Purchase #4	$100.54	3.532%	$104.0911	$104.09	$104.10	$104.10
Purchase #5	$195.89	7.109%	$209.8158	$209.82	$209.80	$209.80
Purchase #6	$216.52	11.589%	$241.6125	$241.61	$241.60	$241.60
Purchase #7	$20.53	7.804%	$22.1322	$22.13	$22.15	$22.10
7 purchase totals =	$742.39		$805.3905	$805.39	$805.35	$805.40