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	$38.35	4.807%	$40.1935	$40.19	$40.20	$40.20
Purchase #2	$244.67	13.176%	$276.9077	$276.91	$276.90	$276.90
Purchase #3	$149.87	5.489%	$158.0964	$158.10	$158.10	$158.10
Purchase #4	$31.29	13.508%	$35.5167	$35.52	$35.50	$35.50
Purchase #5	$98.76	5.449%	$104.1414	$104.14	$104.15	$104.10
Purchase #6	$78.69	6.195%	$83.5648	$83.56	$83.55	$83.60
Purchase #7	$48.76	3.813%	$50.6192	$50.62	$50.60	$50.60
7 purchase totals =	$690.39		$749.0397	$749.04	$749.00	$749.00