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	$78.55	12.134%	$88.0813	$88.08	$88.10	$88.10
Purchase #2	$33.68	10.351%	$37.1662	$37.17	$37.15	$37.20
Purchase #3	$99.47	12.687%	$112.0898	$112.09	$112.10	$112.10
Purchase #4	$16.37	4.645%	$17.1304	$17.13	$17.15	$17.10
Purchase #5	$26.78	6.244%	$28.4521	$28.45	$28.45	$28.50
Purchase #6	$11.39	13.651%	$12.9448	$12.94	$12.95	$12.90
Purchase #7	$37.48	9.277%	$40.957	$40.96	$40.95	$41.00
7 purchase totals =	$303.72		$336.8216	$336.82	$336.85	$336.90