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	$108.62	4.754%	$113.7838	$113.78	$113.80	$113.80
Purchase #2	$87.67	3.576%	$90.8051	$90.81	$90.80	$90.80
Purchase #3	$29.88	11.686%	$33.3718	$33.37	$33.35	$33.40
Purchase #4	$30.91	13.848%	$35.1904	$35.19	$35.20	$35.20
Purchase #5	$204.79	6.750%	$218.6133	$218.61	$218.60	$218.60
Purchase #6	$50.32	6.853%	$53.7684	$53.77	$53.75	$53.80
Purchase #7	$81.66	11.856%	$91.3416	$91.34	$91.35	$91.30
7 purchase totals =	$593.85		$636.8744	$636.87	$636.85	$636.90