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	$69.43	13.229%	$78.6149	$78.61	$78.60	$78.60
Purchase #2	$98.60	5.322%	$103.8475	$103.85	$103.85	$103.80
Purchase #3	$249.83	9.265%	$272.9767	$272.98	$273.00	$273.00
Purchase #4	$138.42	6.321%	$147.1695	$147.17	$147.15	$147.20
Purchase #5	$82.30	8.180%	$89.0321	$89.03	$89.05	$89.00
Purchase #6	$188.84	6.117%	$200.3913	$200.39	$200.40	$200.40
Purchase #7	$248.25	4.635%	$259.7564	$259.76	$259.75	$259.80
7 purchase totals =	$1,075.67		$1,151.7884	$1,151.79	$1,151.80	$1,151.80