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	$158.51	13.872%	$180.4985	$180.50	$180.50	$180.50
Purchase #2	$145.28	5.297%	$152.9755	$152.98	$153.00	$153.00
Purchase #3	$131.60	11.221%	$146.3668	$146.37	$146.35	$146.40
Purchase #4	$99.52	3.800%	$103.3018	$103.30	$103.30	$103.30
Purchase #5	$53.89	9.536%	$59.029	$59.03	$59.05	$59.00
Purchase #6	$36.33	5.230%	$38.2301	$38.23	$38.25	$38.20
Purchase #7	$136.39	10.356%	$150.5145	$150.51	$150.50	$150.50
7 purchase totals =	$761.52		$830.9162	$830.92	$830.95	$830.90