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	$164.88	12.639%	$185.7192	$185.72	$185.70	$185.70
Purchase #2	$247.86	11.452%	$276.2449	$276.24	$276.25	$276.20
Purchase #3	$140.59	12.507%	$158.1736	$158.17	$158.15	$158.20
Purchase #4	$196.76	10.793%	$217.9963	$218.00	$218.00	$218.00
Purchase #5	$57.43	3.176%	$59.254	$59.25	$59.25	$59.30
Purchase #6	$143.83	3.121%	$148.3189	$148.32	$148.30	$148.30
Purchase #7	$153.52	7.775%	$165.4562	$165.46	$165.45	$165.50
7 purchase totals =	$1,104.87		$1,211.1631	$1,211.16	$1,211.10	$1,211.20