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	$88.71	3.248%	$91.5913	$91.59	$91.60	$91.60
Purchase #2	$138.67	4.730%	$145.2291	$145.23	$145.25	$145.20
Purchase #3	$29.47	9.175%	$32.1739	$32.17	$32.15	$32.20
Purchase #4	$119.90	13.552%	$136.1488	$136.15	$136.15	$136.10
Purchase #5	$33.40	5.113%	$35.1077	$35.11	$35.10	$35.10
Purchase #6	$89.57	13.276%	$101.4613	$101.46	$101.45	$101.50
Purchase #7	$14.65	6.716%	$15.6339	$15.63	$15.65	$15.60
7 purchase totals =	$514.37		$557.3460	$557.34	$557.35	$557.30