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	$211.69	9.206%	$231.1782	$231.18	$231.20	$231.20
Purchase #2	$123.35	6.443%	$131.2974	$131.30	$131.30	$131.30
Purchase #3	$210.43	6.260%	$223.6029	$223.60	$223.60	$223.60
Purchase #4	$17.86	10.154%	$19.6735	$19.67	$19.65	$19.70
Purchase #5	$106.73	5.360%	$112.4507	$112.45	$112.45	$112.50
Purchase #6	$192.36	6.209%	$204.3036	$204.30	$204.30	$204.30
Purchase #7	$71.40	7.684%	$76.8864	$76.89	$76.90	$76.90
7 purchase totals =	$933.82		$999.3927	$999.39	$999.40	$999.50