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	$246.97	5.217%	$259.8544	$259.85	$259.85	$259.90
Purchase #2	$243.70	4.854%	$255.5292	$255.53	$255.55	$255.50
Purchase #3	$119.37	12.505%	$134.2972	$134.30	$134.30	$134.30
Purchase #4	$145.65	9.524%	$159.5217	$159.52	$159.50	$159.50
Purchase #5	$135.39	12.104%	$151.7776	$151.78	$151.80	$151.80
Purchase #6	$180.89	3.704%	$187.5902	$187.59	$187.60	$187.60
Purchase #7	$56.78	9.356%	$62.0923	$62.09	$62.10	$62.10
7 purchase totals =	$1,128.75		$1,210.6626	$1,210.66	$1,210.70	$1,210.70