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	$53.78	10.735%	$59.5533	$59.55	$59.55	$59.60
Purchase #2	$79.32	6.371%	$84.3735	$84.37	$84.35	$84.40
Purchase #3	$70.27	11.232%	$78.1627	$78.16	$78.15	$78.20
Purchase #4	$86.40	4.638%	$90.4072	$90.41	$90.40	$90.40
Purchase #5	$113.94	11.858%	$127.451	$127.45	$127.45	$127.50
Purchase #6	$165.59	7.268%	$177.6251	$177.63	$177.65	$177.60
Purchase #7	$184.65	10.232%	$203.5434	$203.54	$203.55	$203.50
7 purchase totals =	$753.95		$821.1162	$821.11	$821.10	$821.20