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	$36.70	12.665%	$41.3481	$41.35	$41.35	$41.30
Purchase #2	$97.32	4.755%	$101.9476	$101.95	$101.95	$101.90
Purchase #3	$37.87	9.761%	$41.5665	$41.57	$41.55	$41.60
Purchase #4	$68.54	5.830%	$72.5359	$72.54	$72.55	$72.50
Purchase #5	$129.26	13.674%	$146.935	$146.94	$146.95	$146.90
Purchase #6	$70.77	6.431%	$75.3212	$75.32	$75.30	$75.30
Purchase #7	$110.43	5.854%	$116.8946	$116.89	$116.90	$116.90
7 purchase totals =	$550.89		$596.5489	$596.56	$596.55	$596.40