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	$150.38	13.328%	$170.4226	$170.42	$170.40	$170.40
Purchase #2	$112.88	3.579%	$116.92	$116.92	$116.90	$116.90
Purchase #3	$93.84	11.363%	$104.503	$104.50	$104.50	$104.50
Purchase #4	$98.93	11.672%	$110.4771	$110.48	$110.50	$110.50
Purchase #5	$146.94	12.693%	$165.5911	$165.59	$165.60	$165.60
Purchase #6	$187.88	6.628%	$200.3327	$200.33	$200.35	$200.30
Purchase #7	$56.36	6.729%	$60.1525	$60.15	$60.15	$60.20
7 purchase totals =	$847.21		$928.3990	$928.39	$928.40	$928.40