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	$134.41	4.832%	$140.9047	$140.90	$140.90	$140.90
Purchase #2	$79.33	12.211%	$89.017	$89.02	$89.00	$89.00
Purchase #3	$157.25	10.234%	$173.343	$173.34	$173.35	$173.30
Purchase #4	$42.35	9.493%	$46.3703	$46.37	$46.35	$46.40
Purchase #5	$57.92	4.492%	$60.5218	$60.52	$60.50	$60.50
Purchase #6	$104.87	13.769%	$119.3096	$119.31	$119.30	$119.30
Purchase #7	$155.37	4.448%	$162.2809	$162.28	$162.30	$162.30
7 purchase totals =	$731.50		$791.7473	$791.74	$791.70	$791.70