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	$240.69	11.680%	$268.8026	$268.80	$268.80	$268.80
Purchase #2	$124.45	6.799%	$132.9114	$132.91	$132.90	$132.90
Purchase #3	$210.54	7.261%	$225.8273	$225.83	$225.85	$225.80
Purchase #4	$90.56	9.481%	$99.146	$99.15	$99.15	$99.10
Purchase #5	$96.33	11.143%	$107.0641	$107.06	$107.05	$107.10
Purchase #6	$205.95	11.301%	$229.2244	$229.22	$229.20	$229.20
Purchase #7	$80.25	3.384%	$82.9657	$82.97	$82.95	$83.00
7 purchase totals =	$1,048.77		$1,145.9415	$1,145.94	$1,145.90	$1,145.90