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	$181.39	13.698%	$206.2368	$206.24	$206.25	$206.20
Purchase #2	$42.73	5.619%	$45.131	$45.13	$45.15	$45.10
Purchase #3	$220.89	6.556%	$235.3715	$235.37	$235.35	$235.40
Purchase #4	$204.81	7.575%	$220.3244	$220.32	$220.30	$220.30
Purchase #5	$57.40	4.420%	$59.9371	$59.94	$59.95	$59.90
Purchase #6	$115.85	12.718%	$130.5838	$130.58	$130.60	$130.60
Purchase #7	$94.98	5.657%	$100.353	$100.35	$100.35	$100.40
7 purchase totals =	$918.05		$997.9376	$997.93	$997.95	$997.90