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	$148.91	10.486%	$164.5247	$164.52	$164.50	$164.50
Purchase #2	$206.58	12.706%	$232.8281	$232.83	$232.85	$232.80
Purchase #3	$17.85	5.551%	$18.8409	$18.84	$18.85	$18.80
Purchase #4	$162.27	10.489%	$179.2905	$179.29	$179.30	$179.30
Purchase #5	$34.74	13.655%	$39.4837	$39.48	$39.50	$39.50
Purchase #6	$19.45	7.301%	$20.87	$20.87	$20.85	$20.90
Purchase #7	$12.81	10.139%	$14.1088	$14.11	$14.10	$14.10
7 purchase totals =	$602.61		$669.9467	$669.94	$669.95	$669.90