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	$23.25	5.140%	$24.4451	$24.45	$24.45	$24.40
Purchase #2	$27.89	7.218%	$29.9031	$29.90	$29.90	$29.90
Purchase #3	$148.46	4.737%	$155.4926	$155.49	$155.50	$155.50
Purchase #4	$55.98	10.508%	$61.8624	$61.86	$61.85	$61.90
Purchase #5	$238.36	11.235%	$265.1397	$265.14	$265.15	$265.10
Purchase #6	$179.36	3.364%	$185.3937	$185.39	$185.40	$185.40
Purchase #7	$166.35	8.624%	$180.696	$180.70	$180.70	$180.70
7 purchase totals =	$839.65		$902.9326	$902.93	$902.95	$902.90