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	$12.55	6.851%	$13.4098	$13.41	$13.40	$13.40
Purchase #2	$38.54	3.784%	$39.9984	$40.00	$40.00	$40.00
Purchase #3	$86.77	4.753%	$90.8942	$90.89	$90.90	$90.90
Purchase #4	$11.93	3.320%	$12.3261	$12.33	$12.35	$12.30
Purchase #5	$61.91	4.378%	$64.6204	$64.62	$64.60	$64.60
Purchase #6	$77.53	7.364%	$83.2393	$83.24	$83.25	$83.20
Purchase #7	$49.28	8.507%	$53.4722	$53.47	$53.45	$53.50
7 purchase totals =	$338.51		$357.9604	$357.96	$357.95	$357.90