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	$115.54	7.427%	$124.1212	$124.12	$124.10	$124.10
Purchase #2	$37.64	7.473%	$40.4528	$40.45	$40.45	$40.50
Purchase #3	$153.48	10.491%	$169.5816	$169.58	$169.60	$169.60
Purchase #4	$32.79	13.711%	$37.2858	$37.29	$37.30	$37.30
Purchase #5	$117.52	11.455%	$130.9819	$130.98	$131.00	$131.00
Purchase #6	$172.78	7.748%	$186.167	$186.17	$186.15	$186.20
Purchase #7	$94.73	9.273%	$103.5143	$103.51	$103.50	$103.50
7 purchase totals =	$724.48		$792.1046	$792.10	$792.10	$792.20