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	$71.67	13.804%	$81.5633	$81.56	$81.55	$81.60
Purchase #2	$79.84	13.757%	$90.8236	$90.82	$90.80	$90.80
Purchase #3	$43.94	4.634%	$45.9762	$45.98	$46.00	$46.00
Purchase #4	$194.77	5.435%	$205.3557	$205.36	$205.35	$205.40
Purchase #5	$112.80	7.169%	$120.8866	$120.89	$120.90	$120.90
Purchase #6	$99.54	11.333%	$110.8209	$110.82	$110.80	$110.80
Purchase #7	$243.45	7.828%	$262.5073	$262.51	$262.50	$262.50
7 purchase totals =	$846.01		$917.9336	$917.94	$917.90	$918.00