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	$36.76	10.528%	$40.6301	$40.63	$40.65	$40.60
Purchase #2	$55.51	3.376%	$57.384	$57.38	$57.40	$57.40
Purchase #3	$156.50	13.773%	$178.0547	$178.05	$178.05	$178.10
Purchase #4	$78.40	8.451%	$85.0256	$85.03	$85.05	$85.00
Purchase #5	$97.35	6.185%	$103.3711	$103.37	$103.35	$103.40
Purchase #6	$243.69	7.326%	$261.5427	$261.54	$261.55	$261.50
Purchase #7	$181.58	11.766%	$202.9447	$202.94	$202.95	$202.90
7 purchase totals =	$849.79		$928.9529	$928.94	$929.00	$928.90