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	$158.64	6.265%	$168.5788	$168.58	$168.60	$168.60
Purchase #2	$53.92	10.730%	$59.7056	$59.71	$59.70	$59.70
Purchase #3	$234.35	3.566%	$242.7069	$242.71	$242.70	$242.70
Purchase #4	$153.54	3.604%	$159.0736	$159.07	$159.05	$159.10
Purchase #5	$32.55	12.285%	$36.5488	$36.55	$36.55	$36.50
Purchase #6	$24.51	10.802%	$27.1576	$27.16	$27.15	$27.20
Purchase #7	$88.33	12.702%	$99.5497	$99.55	$99.55	$99.50
7 purchase totals =	$745.84		$793.3210	$793.33	$793.30	$793.30