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	$225.30	6.821%	$240.6677	$240.67	$240.65	$240.70
Purchase #2	$48.48	5.573%	$51.1818	$51.18	$51.20	$51.20
Purchase #3	$45.54	13.228%	$51.564	$51.56	$51.55	$51.60
Purchase #4	$40.44	9.243%	$44.1779	$44.18	$44.20	$44.20
Purchase #5	$52.97	11.660%	$59.1463	$59.15	$59.15	$59.10
Purchase #6	$80.66	11.759%	$90.1448	$90.14	$90.15	$90.10
Purchase #7	$149.60	12.234%	$167.9021	$167.90	$167.90	$167.90
7 purchase totals =	$642.99		$704.7846	$704.78	$704.80	$704.80