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	$157.66	4.305%	$164.4473	$164.45	$164.45	$164.40
Purchase #2	$17.83	5.636%	$18.8349	$18.83	$18.85	$18.80
Purchase #3	$225.60	3.624%	$233.7757	$233.78	$233.80	$233.80
Purchase #4	$30.59	8.357%	$33.1464	$33.15	$33.15	$33.10
Purchase #5	$66.32	4.599%	$69.3701	$69.37	$69.35	$69.40
Purchase #6	$16.79	12.229%	$18.8432	$18.84	$18.85	$18.80
Purchase #7	$120.76	7.199%	$129.4535	$129.45	$129.45	$129.50
7 purchase totals =	$635.55		$667.8711	$667.87	$667.90	$667.80