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	$162.57	6.683%	$173.4346	$173.43	$173.45	$173.40
Purchase #2	$241.54	4.787%	$253.1025	$253.10	$253.10	$253.10
Purchase #3	$116.72	13.200%	$132.127	$132.13	$132.15	$132.10
Purchase #4	$115.31	7.507%	$123.9663	$123.97	$123.95	$124.00
Purchase #5	$94.61	9.408%	$103.5109	$103.51	$103.50	$103.50
Purchase #6	$219.93	12.415%	$247.2343	$247.23	$247.25	$247.20
Purchase #7	$235.49	12.754%	$265.5244	$265.52	$265.50	$265.50
7 purchase totals =	$1,186.17		$1,298.9000	$1,298.89	$1,298.90	$1,298.80