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	$250.34	4.229%	$260.9269	$260.93	$260.95	$260.90
Purchase #2	$95.68	10.548%	$105.7723	$105.77	$105.75	$105.80
Purchase #3	$216.25	10.437%	$238.82	$238.82	$238.80	$238.80
Purchase #4	$141.50	6.383%	$150.5319	$150.53	$150.55	$150.50
Purchase #5	$173.41	12.848%	$195.6897	$195.69	$195.70	$195.70
Purchase #6	$33.37	12.786%	$37.6367	$37.64	$37.65	$37.60
Purchase #7	$28.64	3.717%	$29.7045	$29.70	$29.70	$29.70
7 purchase totals =	$939.19		$1,019.0820	$1,019.08	$1,019.10	$1,019.00