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	$9.71	6.677%	$10.3583	$10.36	$10.35	$10.40
Purchase #2	$84.51	7.613%	$90.9437	$90.94	$90.95	$90.90
Purchase #3	$245.77	8.193%	$265.9059	$265.91	$265.90	$265.90
Purchase #4	$189.91	10.313%	$209.4954	$209.50	$209.50	$209.50
Purchase #5	$167.88	10.860%	$186.1118	$186.11	$186.10	$186.10
Purchase #6	$175.85	7.379%	$188.826	$188.83	$188.85	$188.80
Purchase #7	$214.41	9.552%	$234.8904	$234.89	$234.90	$234.90
7 purchase totals =	$1,088.04		$1,186.5315	$1,186.54	$1,186.55	$1,186.50