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	$93.29	8.818%	$101.5163	$101.52	$101.50	$101.50
Purchase #2	$204.37	12.140%	$229.1805	$229.18	$229.20	$229.20
Purchase #3	$92.72	9.420%	$101.4542	$101.45	$101.45	$101.50
Purchase #4	$57.35	12.690%	$64.6277	$64.63	$64.65	$64.60
Purchase #5	$128.89	6.754%	$137.5952	$137.60	$137.60	$137.60
Purchase #6	$174.76	7.438%	$187.7586	$187.76	$187.75	$187.80
Purchase #7	$36.58	4.722%	$38.3073	$38.31	$38.30	$38.30
7 purchase totals =	$787.96		$860.4398	$860.45	$860.45	$860.50