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	$36.85	6.493%	$39.2427	$39.24	$39.25	$39.20
Purchase #2	$65.71	3.728%	$68.1597	$68.16	$68.15	$68.20
Purchase #3	$188.53	5.141%	$198.2223	$198.22	$198.20	$198.20
Purchase #4	$67.82	4.775%	$71.0584	$71.06	$71.05	$71.10
Purchase #5	$186.76	12.235%	$209.6101	$209.61	$209.60	$209.60
Purchase #6	$97.30	8.158%	$105.2377	$105.24	$105.25	$105.20
Purchase #7	$220.34	13.607%	$250.3217	$250.32	$250.30	$250.30
7 purchase totals =	$863.31		$941.8526	$941.85	$941.80	$941.80