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	$146.39	13.611%	$166.3151	$166.32	$166.30	$166.30
Purchase #2	$29.26	7.308%	$31.3983	$31.40	$31.40	$31.40
Purchase #3	$99.94	4.134%	$104.0715	$104.07	$104.05	$104.10
Purchase #4	$235.26	10.173%	$259.193	$259.19	$259.20	$259.20
Purchase #5	$75.52	3.719%	$78.3286	$78.33	$78.35	$78.30
Purchase #6	$237.50	11.787%	$265.4941	$265.49	$265.50	$265.50
Purchase #7	$115.90	13.172%	$131.1663	$131.17	$131.15	$131.20
7 purchase totals =	$939.77		$1,035.9669	$1,035.97	$1,035.95	$1,036.00