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	$37.87	4.114%	$39.428	$39.43	$39.45	$39.40
Purchase #2	$239.54	7.244%	$256.8923	$256.89	$256.90	$256.90
Purchase #3	$7.97	5.339%	$8.3955	$8.40	$8.40	$8.40
Purchase #4	$246.66	10.613%	$272.838	$272.84	$272.85	$272.80
Purchase #5	$59.89	3.723%	$62.1197	$62.12	$62.10	$62.10
Purchase #6	$58.72	11.227%	$65.3125	$65.31	$65.30	$65.30
Purchase #7	$27.86	12.213%	$31.2625	$31.26	$31.25	$31.30
7 purchase totals =	$678.51		$736.2485	$736.25	$736.25	$736.20