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	$11.80	4.209%	$12.2967	$12.30	$12.30	$12.30
Purchase #2	$114.69	11.351%	$127.7085	$127.71	$127.70	$127.70
Purchase #3	$87.92	13.305%	$99.6178	$99.62	$99.60	$99.60
Purchase #4	$155.97	7.814%	$168.1575	$168.16	$168.15	$168.20
Purchase #5	$223.26	9.685%	$244.8827	$244.88	$244.90	$244.90
Purchase #6	$182.97	9.792%	$200.8864	$200.89	$200.90	$200.90
Purchase #7	$38.36	4.233%	$39.9838	$39.98	$40.00	$40.00
7 purchase totals =	$814.97		$893.5334	$893.54	$893.55	$893.60