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	$101.84	3.663%	$105.5704	$105.57	$105.55	$105.60
Purchase #2	$228.85	5.785%	$242.089	$242.09	$242.10	$242.10
Purchase #3	$156.45	6.469%	$166.5708	$166.57	$166.55	$166.60
Purchase #4	$47.34	7.414%	$50.8498	$50.85	$50.85	$50.80
Purchase #5	$86.78	3.761%	$90.0438	$90.04	$90.05	$90.00
Purchase #6	$108.29	4.446%	$113.1046	$113.10	$113.10	$113.10
Purchase #7	$15.62	3.426%	$16.1551	$16.16	$16.15	$16.20
7 purchase totals =	$745.17		$784.3835	$784.38	$784.35	$784.40