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	$13.65	4.406%	$14.2514	$14.25	$14.25	$14.30
Purchase #2	$153.77	8.277%	$166.4975	$166.50	$166.50	$166.50
Purchase #3	$42.84	10.386%	$47.2894	$47.29	$47.30	$47.30
Purchase #4	$41.33	8.525%	$44.8534	$44.85	$44.85	$44.90
Purchase #5	$83.46	7.125%	$89.4065	$89.41	$89.40	$89.40
Purchase #6	$142.93	6.199%	$151.7902	$151.79	$151.80	$151.80
Purchase #7	$63.54	7.490%	$68.2991	$68.30	$68.30	$68.30
7 purchase totals =	$541.52		$582.3875	$582.39	$582.40	$582.50