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	$152.94	3.229%	$157.8784	$157.88	$157.90	$157.90
Purchase #2	$39.80	13.808%	$45.2956	$45.30	$45.30	$45.30
Purchase #3	$108.59	4.512%	$113.4896	$113.49	$113.50	$113.50
Purchase #4	$71.86	5.214%	$75.6068	$75.61	$75.60	$75.60
Purchase #5	$95.49	4.153%	$99.4557	$99.46	$99.45	$99.50
Purchase #6	$159.60	11.770%	$178.3849	$178.38	$178.40	$178.40
Purchase #7	$19.72	6.382%	$20.9785	$20.98	$21.00	$21.00
7 purchase totals =	$648.00		$691.0895	$691.10	$691.15	$691.20