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	$13.57	12.395%	$15.252	$15.25	$15.25	$15.30
Purchase #2	$38.37	7.221%	$41.1407	$41.14	$41.15	$41.10
Purchase #3	$101.41	3.866%	$105.3305	$105.33	$105.35	$105.30
Purchase #4	$244.61	6.602%	$260.7592	$260.76	$260.75	$260.80
Purchase #5	$134.73	10.449%	$148.8079	$148.81	$148.80	$148.80
Purchase #6	$82.75	3.200%	$85.398	$85.40	$85.40	$85.40
Purchase #7	$133.32	4.386%	$139.1674	$139.17	$139.15	$139.20
7 purchase totals =	$748.76		$795.8557	$795.86	$795.85	$795.90