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	$135.78	13.361%	$153.9216	$153.92	$153.90	$153.90
Purchase #2	$33.89	11.776%	$37.8809	$37.88	$37.90	$37.90
Purchase #3	$61.75	7.139%	$66.1583	$66.16	$66.15	$66.20
Purchase #4	$61.54	10.641%	$68.0885	$68.09	$68.10	$68.10
Purchase #5	$182.95	8.680%	$198.8301	$198.83	$198.85	$198.80
Purchase #6	$37.48	11.394%	$41.7505	$41.75	$41.75	$41.80
Purchase #7	$78.86	3.535%	$81.6477	$81.65	$81.65	$81.60
7 purchase totals =	$592.25		$648.2776	$648.28	$648.30	$648.30