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	$16.61	8.768%	$18.0664	$18.07	$18.05	$18.10
Purchase #2	$226.74	6.255%	$240.9226	$240.92	$240.90	$240.90
Purchase #3	$65.73	8.468%	$71.296	$71.30	$71.30	$71.30
Purchase #4	$37.89	13.405%	$42.9692	$42.97	$42.95	$43.00
Purchase #5	$80.59	12.480%	$90.6476	$90.65	$90.65	$90.60
Purchase #6	$46.39	9.766%	$50.9204	$50.92	$50.90	$50.90
Purchase #7	$71.68	13.116%	$81.0815	$81.08	$81.10	$81.10
7 purchase totals =	$545.63		$595.9037	$595.91	$595.85	$595.90