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	$119.71	9.660%	$131.274	$131.27	$131.25	$131.30
Purchase #2	$125.62	10.109%	$138.3189	$138.32	$138.30	$138.30
Purchase #3	$29.66	12.295%	$33.3067	$33.31	$33.30	$33.30
Purchase #4	$29.95	5.790%	$31.6841	$31.68	$31.70	$31.70
Purchase #5	$18.50	6.129%	$19.6339	$19.63	$19.65	$19.60
Purchase #6	$51.30	3.388%	$53.038	$53.04	$53.05	$53.00
Purchase #7	$179.85	6.694%	$191.8892	$191.89	$191.90	$191.90
7 purchase totals =	$554.59		$599.1448	$599.14	$599.15	$599.10