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	$94.25	9.478%	$103.183	$103.18	$103.20	$103.20
Purchase #2	$33.81	4.686%	$35.3943	$35.39	$35.40	$35.40
Purchase #3	$55.36	5.224%	$58.252	$58.25	$58.25	$58.30
Purchase #4	$63.83	13.240%	$72.2811	$72.28	$72.30	$72.30
Purchase #5	$177.70	10.667%	$196.6553	$196.66	$196.65	$196.70
Purchase #6	$223.42	3.687%	$231.6575	$231.66	$231.65	$231.70
Purchase #7	$136.81	6.389%	$145.5508	$145.55	$145.55	$145.60
7 purchase totals =	$785.18		$842.9740	$842.97	$843.00	$843.20