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	$34.95	12.785%	$39.4184	$39.42	$39.40	$39.40
Purchase #2	$40.87	11.166%	$45.4335	$45.43	$45.45	$45.40
Purchase #3	$219.60	10.387%	$242.4099	$242.41	$242.40	$242.40
Purchase #4	$145.44	9.199%	$158.819	$158.82	$158.80	$158.80
Purchase #5	$235.62	7.627%	$253.5907	$253.59	$253.60	$253.60
Purchase #6	$219.57	12.645%	$247.3346	$247.33	$247.35	$247.30
Purchase #7	$39.64	12.168%	$44.4634	$44.46	$44.45	$44.50
7 purchase totals =	$935.69		$1,031.4695	$1,031.46	$1,031.45	$1,031.40