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	$249.31	3.589%	$258.2577	$258.26	$258.25	$258.30
Purchase #2	$87.75	4.221%	$91.4539	$91.45	$91.45	$91.50
Purchase #3	$117.51	7.639%	$126.4866	$126.49	$126.50	$126.50
Purchase #4	$131.28	9.651%	$143.9498	$143.95	$143.95	$143.90
Purchase #5	$98.37	4.366%	$102.6648	$102.66	$102.65	$102.70
Purchase #6	$32.76	7.855%	$35.3333	$35.33	$35.35	$35.30
Purchase #7	$99.75	10.138%	$109.8627	$109.86	$109.85	$109.90
7 purchase totals =	$816.73		$868.0088	$868.00	$868.00	$868.10