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	$148.30	11.599%	$165.5013	$165.50	$165.50	$165.50
Purchase #2	$39.58	7.715%	$42.6336	$42.63	$42.65	$42.60
Purchase #3	$193.93	12.187%	$217.5642	$217.56	$217.55	$217.60
Purchase #4	$151.67	11.604%	$169.2698	$169.27	$169.25	$169.30
Purchase #5	$58.56	12.494%	$65.8765	$65.88	$65.90	$65.90
Purchase #6	$147.28	5.602%	$155.5306	$155.53	$155.55	$155.50
Purchase #7	$30.49	6.393%	$32.4392	$32.44	$32.45	$32.40
7 purchase totals =	$769.81		$848.8152	$848.81	$848.85	$848.80