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	$21.50	13.531%	$24.4092	$24.41	$24.40	$24.40
Purchase #2	$106.39	6.775%	$113.5979	$113.60	$113.60	$113.60
Purchase #3	$150.81	7.406%	$161.979	$161.98	$162.00	$162.00
Purchase #4	$162.31	8.121%	$175.4912	$175.49	$175.50	$175.50
Purchase #5	$162.43	5.316%	$171.0648	$171.06	$171.05	$171.10
Purchase #6	$87.89	4.322%	$91.6886	$91.69	$91.70	$91.70
Purchase #7	$105.27	7.641%	$113.3137	$113.31	$113.30	$113.30
7 purchase totals =	$796.60		$851.5444	$851.54	$851.55	$851.60