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	$11.46	13.233%	$12.9765	$12.98	$13.00	$13.00
Purchase #2	$218.75	12.153%	$245.3347	$245.33	$245.35	$245.30
Purchase #3	$250.31	4.862%	$262.4801	$262.48	$262.50	$262.50
Purchase #4	$114.59	12.549%	$128.9699	$128.97	$128.95	$129.00
Purchase #5	$146.50	4.751%	$153.4602	$153.46	$153.45	$153.50
Purchase #6	$106.49	4.777%	$111.577	$111.58	$111.60	$111.60
Purchase #7	$27.50	8.819%	$29.9252	$29.93	$29.95	$29.90
7 purchase totals =	$875.60		$944.7236	$944.73	$944.80	$944.80