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	$122.33	7.703%	$131.7531	$131.75	$131.75	$131.80
Purchase #2	$164.60	3.596%	$170.519	$170.52	$170.50	$170.50
Purchase #3	$98.79	6.143%	$104.8587	$104.86	$104.85	$104.90
Purchase #4	$31.66	5.798%	$33.4956	$33.50	$33.50	$33.50
Purchase #5	$62.78	10.648%	$69.4648	$69.46	$69.45	$69.50
Purchase #6	$11.69	3.179%	$12.0616	$12.06	$12.05	$12.10
Purchase #7	$150.32	11.230%	$167.2009	$167.20	$167.20	$167.20
7 purchase totals =	$642.17		$689.3537	$689.35	$689.30	$689.50