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	$112.69	6.760%	$120.3078	$120.31	$120.30	$120.30
Purchase #2	$45.75	11.597%	$51.0556	$51.06	$51.05	$51.10
Purchase #3	$227.86	6.403%	$242.4499	$242.45	$242.45	$242.40
Purchase #4	$11.91	7.661%	$12.8224	$12.82	$12.80	$12.80
Purchase #5	$160.31	4.368%	$167.3123	$167.31	$167.30	$167.30
Purchase #6	$196.79	10.257%	$216.9748	$216.97	$216.95	$217.00
Purchase #7	$96.83	13.364%	$109.7704	$109.77	$109.75	$109.80
7 purchase totals =	$852.14		$920.6932	$920.69	$920.60	$920.70