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	$112.76	10.750%	$124.8817	$124.88	$124.90	$124.90
Purchase #2	$81.55	10.838%	$90.3884	$90.39	$90.40	$90.40
Purchase #3	$153.79	13.793%	$175.0023	$175.00	$175.00	$175.00
Purchase #4	$43.93	8.484%	$47.657	$47.66	$47.65	$47.70
Purchase #5	$47.75	13.566%	$54.2278	$54.23	$54.25	$54.20
Purchase #6	$210.77	5.595%	$222.5626	$222.56	$222.55	$222.60
Purchase #7	$74.82	5.444%	$78.8932	$78.89	$78.90	$78.90
7 purchase totals =	$725.37		$793.6130	$793.61	$793.65	$793.70