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	$163.80	10.360%	$180.7697	$180.77	$180.75	$180.80
Purchase #2	$84.31	7.125%	$90.3171	$90.32	$90.30	$90.30
Purchase #3	$138.76	9.863%	$152.4459	$152.45	$152.45	$152.40
Purchase #4	$51.84	13.788%	$58.9877	$58.99	$59.00	$59.00
Purchase #5	$31.47	4.508%	$32.8887	$32.89	$32.90	$32.90
Purchase #6	$146.44	6.528%	$155.9996	$156.00	$156.00	$156.00
Purchase #7	$116.25	12.625%	$130.9266	$130.93	$130.95	$130.90
7 purchase totals =	$732.87		$802.3353	$802.35	$802.35	$802.30