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	$45.95	10.684%	$50.8593	$50.86	$50.85	$50.90
Purchase #2	$29.88	8.610%	$32.4527	$32.45	$32.45	$32.50
Purchase #3	$24.79	11.622%	$27.6711	$27.67	$27.65	$27.70
Purchase #4	$238.85	13.202%	$270.383	$270.38	$270.40	$270.40
Purchase #5	$234.37	3.464%	$242.4886	$242.49	$242.50	$242.50
Purchase #6	$54.95	13.310%	$62.2638	$62.26	$62.25	$62.30
Purchase #7	$64.37	6.298%	$68.424	$68.42	$68.40	$68.40
7 purchase totals =	$693.16		$754.5425	$754.53	$754.50	$754.70