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	$77.70	7.296%	$83.369	$83.37	$83.35	$83.40
Purchase #2	$114.26	12.431%	$128.4637	$128.46	$128.45	$128.50
Purchase #3	$180.42	3.159%	$186.1195	$186.12	$186.10	$186.10
Purchase #4	$99.52	4.716%	$104.2134	$104.21	$104.20	$104.20
Purchase #5	$42.77	13.732%	$48.6432	$48.64	$48.65	$48.60
Purchase #6	$37.32	5.786%	$39.4793	$39.48	$39.50	$39.50
Purchase #7	$11.54	11.873%	$12.9101	$12.91	$12.90	$12.90
7 purchase totals =	$563.53		$603.1982	$603.19	$603.15	$603.20