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	$22.78	12.259%	$25.5726	$25.57	$25.55	$25.60
Purchase #2	$99.69	5.390%	$105.0633	$105.06	$105.05	$105.10
Purchase #3	$58.31	13.376%	$66.1095	$66.11	$66.10	$66.10
Purchase #4	$79.67	12.773%	$89.8462	$89.85	$89.85	$89.80
Purchase #5	$46.48	7.611%	$50.0176	$50.02	$50.00	$50.00
Purchase #6	$119.29	10.813%	$132.1888	$132.19	$132.20	$132.20
Purchase #7	$94.73	9.195%	$103.4404	$103.44	$103.45	$103.40
7 purchase totals =	$520.95		$572.2384	$572.24	$572.20	$572.20