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	$43.96	11.211%	$48.8884	$48.89	$48.90	$48.90
Purchase #2	$96.78	12.646%	$109.0188	$109.02	$109.00	$109.00
Purchase #3	$19.89	6.176%	$21.1184	$21.12	$21.10	$21.10
Purchase #4	$162.63	5.102%	$170.9274	$170.93	$170.95	$170.90
Purchase #5	$7.31	11.613%	$8.1589	$8.16	$8.15	$8.20
Purchase #6	$109.49	12.450%	$123.1215	$123.12	$123.10	$123.10
Purchase #7	$145.62	11.512%	$162.3838	$162.38	$162.40	$162.40
7 purchase totals =	$585.68		$643.6172	$643.62	$643.60	$643.60