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	$128.93	3.317%	$133.2066	$133.21	$133.20	$133.20
Purchase #2	$18.59	13.685%	$21.134	$21.13	$21.15	$21.10
Purchase #3	$162.52	3.524%	$168.2472	$168.25	$168.25	$168.20
Purchase #4	$71.58	7.451%	$76.9134	$76.91	$76.90	$76.90
Purchase #5	$139.70	12.368%	$156.9781	$156.98	$157.00	$157.00
Purchase #6	$65.68	11.534%	$73.2555	$73.26	$73.25	$73.30
Purchase #7	$37.85	13.267%	$42.8716	$42.87	$42.85	$42.90
7 purchase totals =	$624.85		$672.6064	$672.61	$672.60	$672.60