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	$120.78	6.240%	$128.3167	$128.32	$128.30	$128.30
Purchase #2	$52.32	6.712%	$55.8317	$55.83	$55.85	$55.80
Purchase #3	$161.85	12.761%	$182.5037	$182.50	$182.50	$182.50
Purchase #4	$62.42	12.602%	$70.2862	$70.29	$70.30	$70.30
Purchase #5	$164.72	9.393%	$180.1921	$180.19	$180.20	$180.20
Purchase #6	$90.45	9.728%	$99.249	$99.25	$99.25	$99.20
Purchase #7	$43.30	8.511%	$46.9853	$46.99	$47.00	$47.00
7 purchase totals =	$695.84		$763.3647	$763.37	$763.40	$763.30