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	$179.76	3.777%	$186.5495	$186.55	$186.55	$186.50
Purchase #2	$222.77	4.154%	$232.0239	$232.02	$232.00	$232.00
Purchase #3	$35.63	5.498%	$37.5889	$37.59	$37.60	$37.60
Purchase #4	$172.78	7.216%	$185.2478	$185.25	$185.25	$185.20
Purchase #5	$55.89	6.308%	$59.4155	$59.42	$59.40	$59.40
Purchase #6	$117.87	11.542%	$131.4746	$131.47	$131.45	$131.50
Purchase #7	$46.88	8.776%	$50.9942	$50.99	$51.00	$51.00
7 purchase totals =	$831.58		$883.2944	$883.29	$883.25	$883.20