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	$241.41	5.436%	$254.533	$254.53	$254.55	$254.50
Purchase #2	$123.74	13.663%	$140.6466	$140.65	$140.65	$140.60
Purchase #3	$235.38	12.230%	$264.167	$264.17	$264.15	$264.20
Purchase #4	$13.86	11.671%	$15.4776	$15.48	$15.50	$15.50
Purchase #5	$8.93	7.403%	$9.5911	$9.59	$9.60	$9.60
Purchase #6	$53.73	11.393%	$59.8515	$59.85	$59.85	$59.90
Purchase #7	$95.99	6.560%	$102.2869	$102.29	$102.30	$102.30
7 purchase totals =	$773.04		$846.5537	$846.56	$846.60	$846.60