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	$88.46	13.661%	$100.5445	$100.54	$100.55	$100.50
Purchase #2	$246.33	7.329%	$264.3835	$264.38	$264.40	$264.40
Purchase #3	$139.27	6.534%	$148.3699	$148.37	$148.35	$148.40
Purchase #4	$105.85	4.382%	$110.4883	$110.49	$110.50	$110.50
Purchase #5	$14.89	6.757%	$15.8961	$15.90	$15.90	$15.90
Purchase #6	$65.79	12.125%	$73.767	$73.77	$73.75	$73.80
Purchase #7	$217.47	10.262%	$239.7868	$239.79	$239.80	$239.80
7 purchase totals =	$878.06		$953.2361	$953.24	$953.25	$953.30