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	$106.55	9.505%	$116.6776	$116.68	$116.70	$116.70
Purchase #2	$151.78	13.548%	$172.3432	$172.34	$172.35	$172.30
Purchase #3	$24.76	10.268%	$27.3024	$27.30	$27.30	$27.30
Purchase #4	$244.30	11.146%	$271.5297	$271.53	$271.55	$271.50
Purchase #5	$96.61	5.664%	$102.082	$102.08	$102.10	$102.10
Purchase #6	$71.37	3.537%	$73.8944	$73.89	$73.90	$73.90
Purchase #7	$124.80	12.671%	$140.6134	$140.61	$140.60	$140.60
7 purchase totals =	$820.17		$904.4427	$904.43	$904.50	$904.40