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	$129.78	7.472%	$139.4772	$139.48	$139.50	$139.50
Purchase #2	$20.98	11.600%	$23.4137	$23.41	$23.40	$23.40
Purchase #3	$78.76	8.842%	$85.724	$85.72	$85.70	$85.70
Purchase #4	$69.72	12.464%	$78.4099	$78.41	$78.40	$78.40
Purchase #5	$246.29	7.163%	$263.9318	$263.93	$263.95	$263.90
Purchase #6	$11.25	13.745%	$12.7963	$12.80	$12.80	$12.80
Purchase #7	$29.84	6.460%	$31.7677	$31.77	$31.75	$31.80
7 purchase totals =	$586.62		$635.5206	$635.52	$635.50	$635.50