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	$37.86	11.410%	$42.1798	$42.18	$42.20	$42.20
Purchase #2	$120.57	5.619%	$127.3448	$127.34	$127.35	$127.30
Purchase #3	$6.56	10.453%	$7.2457	$7.25	$7.25	$7.20
Purchase #4	$119.50	4.177%	$124.4915	$124.49	$124.50	$124.50
Purchase #5	$30.76	11.536%	$34.3085	$34.31	$34.30	$34.30
Purchase #6	$45.54	3.676%	$47.2141	$47.21	$47.20	$47.20
Purchase #7	$40.93	8.774%	$44.5212	$44.52	$44.50	$44.50
7 purchase totals =	$401.72		$427.3056	$427.30	$427.30	$427.20