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	$188.83	7.169%	$202.3672	$202.37	$202.35	$202.40
Purchase #2	$145.69	11.720%	$162.7649	$162.76	$162.75	$162.80
Purchase #3	$208.49	7.391%	$223.8995	$223.90	$223.90	$223.90
Purchase #4	$226.55	12.562%	$255.0092	$255.01	$255.00	$255.00
Purchase #5	$242.86	5.229%	$255.5591	$255.56	$255.55	$255.60
Purchase #6	$31.48	10.554%	$34.8024	$34.80	$34.80	$34.80
Purchase #7	$51.58	5.499%	$54.4164	$54.42	$54.40	$54.40
7 purchase totals =	$1,095.48		$1,188.8187	$1,188.82	$1,188.75	$1,188.90