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	$149.64	8.514%	$162.3803	$162.38	$162.40	$162.40
Purchase #2	$60.81	11.713%	$67.9327	$67.93	$67.95	$67.90
Purchase #3	$38.67	10.639%	$42.7841	$42.78	$42.80	$42.80
Purchase #4	$166.84	5.793%	$176.505	$176.51	$176.50	$176.50
Purchase #5	$5.99	7.527%	$6.4409	$6.44	$6.45	$6.40
Purchase #6	$11.25	10.222%	$12.4	$12.40	$12.40	$12.40
Purchase #7	$19.38	3.413%	$20.0414	$20.04	$20.05	$20.00
7 purchase totals =	$452.58		$488.4844	$488.48	$488.55	$488.40