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	$152.65	3.862%	$158.5453	$158.55	$158.55	$158.50
Purchase #2	$5.58	12.414%	$6.2727	$6.27	$6.25	$6.30
Purchase #3	$178.38	11.453%	$198.8099	$198.81	$198.80	$198.80
Purchase #4	$53.40	7.420%	$57.3623	$57.36	$57.35	$57.40
Purchase #5	$40.97	4.272%	$42.7202	$42.72	$42.70	$42.70
Purchase #6	$31.64	7.142%	$33.8997	$33.90	$33.90	$33.90
Purchase #7	$47.85	9.444%	$52.369	$52.37	$52.35	$52.40
7 purchase totals =	$510.47		$549.9791	$549.98	$549.90	$550.00