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	$127.72	12.272%	$143.3938	$143.39	$143.40	$143.40
Purchase #2	$124.89	10.223%	$137.6575	$137.66	$137.65	$137.70
Purchase #3	$67.53	13.736%	$76.8059	$76.81	$76.80	$76.80
Purchase #4	$53.69	3.154%	$55.3834	$55.38	$55.40	$55.40
Purchase #5	$121.96	4.392%	$127.3165	$127.32	$127.30	$127.30
Purchase #6	$72.30	3.649%	$74.9382	$74.94	$74.95	$74.90
Purchase #7	$165.52	7.479%	$177.8992	$177.90	$177.90	$177.90
7 purchase totals =	$733.61		$793.3945	$793.40	$793.40	$793.40