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	$45.77	8.612%	$49.7117	$49.71	$49.70	$49.70
Purchase #2	$249.94	10.384%	$275.8938	$275.89	$275.90	$275.90
Purchase #3	$66.78	3.484%	$69.1066	$69.11	$69.10	$69.10
Purchase #4	$129.86	9.268%	$141.8954	$141.90	$141.90	$141.90
Purchase #5	$58.83	9.715%	$64.5453	$64.55	$64.55	$64.50
Purchase #6	$178.58	6.326%	$189.877	$189.88	$189.90	$189.90
Purchase #7	$65.33	10.657%	$72.2922	$72.29	$72.30	$72.30
7 purchase totals =	$795.09		$863.3220	$863.33	$863.35	$863.30