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	$89.30	10.109%	$98.3273	$98.33	$98.35	$98.30
Purchase #2	$178.98	3.202%	$184.7109	$184.71	$184.70	$184.70
Purchase #3	$28.62	9.332%	$31.2908	$31.29	$31.30	$31.30
Purchase #4	$137.51	5.679%	$145.3192	$145.32	$145.30	$145.30
Purchase #5	$9.55	6.452%	$10.1662	$10.17	$10.15	$10.20
Purchase #6	$88.32	11.657%	$98.6155	$98.62	$98.60	$98.60
Purchase #7	$97.32	3.143%	$100.3788	$100.38	$100.40	$100.40
7 purchase totals =	$629.60		$668.8087	$668.82	$668.80	$668.80