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	$107.58	8.284%	$116.4919	$116.49	$116.50	$116.50
Purchase #2	$74.27	12.308%	$83.4112	$83.41	$83.40	$83.40
Purchase #3	$85.76	11.392%	$95.5298	$95.53	$95.55	$95.50
Purchase #4	$66.41	5.197%	$69.8613	$69.86	$69.85	$69.90
Purchase #5	$54.56	13.843%	$62.1127	$62.11	$62.10	$62.10
Purchase #6	$7.86	6.135%	$8.3422	$8.34	$8.35	$8.30
Purchase #7	$207.47	11.799%	$231.9494	$231.95	$231.95	$231.90
7 purchase totals =	$603.91		$667.6985	$667.69	$667.70	$667.60