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	$79.97	11.275%	$88.9866	$88.99	$89.00	$89.00
Purchase #2	$135.66	12.158%	$152.1535	$152.15	$152.15	$152.20
Purchase #3	$56.47	4.675%	$59.11	$59.11	$59.10	$59.10
Purchase #4	$234.55	9.291%	$256.342	$256.34	$256.35	$256.30
Purchase #5	$86.25	3.580%	$89.3378	$89.34	$89.35	$89.30
Purchase #6	$237.67	11.790%	$265.6913	$265.69	$265.70	$265.70
Purchase #7	$155.50	8.569%	$168.8248	$168.82	$168.80	$168.80
7 purchase totals =	$986.07		$1,080.4460	$1,080.44	$1,080.45	$1,080.40