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	$50.89	5.656%	$53.7683	$53.77	$53.75	$53.80
Purchase #2	$119.29	4.844%	$125.0684	$125.07	$125.05	$125.10
Purchase #3	$227.47	6.205%	$241.5845	$241.58	$241.60	$241.60
Purchase #4	$56.69	5.565%	$59.8448	$59.84	$59.85	$59.80
Purchase #5	$125.53	3.864%	$130.3805	$130.38	$130.40	$130.40
Purchase #6	$35.82	13.179%	$40.5407	$40.54	$40.55	$40.50
Purchase #7	$5.80	4.131%	$6.0396	$6.04	$6.05	$6.00
7 purchase totals =	$621.49		$657.2268	$657.22	$657.25	$657.20