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	$82.37	9.214%	$89.9596	$89.96	$89.95	$90.00
Purchase #2	$236.71	10.761%	$262.1824	$262.18	$262.20	$262.20
Purchase #3	$155.34	13.308%	$176.0126	$176.01	$176.00	$176.00
Purchase #4	$158.39	4.255%	$165.1295	$165.13	$165.15	$165.10
Purchase #5	$212.25	3.578%	$219.8443	$219.84	$219.85	$219.80
Purchase #6	$6.78	8.253%	$7.3396	$7.34	$7.35	$7.30
Purchase #7	$154.57	3.410%	$159.8408	$159.84	$159.85	$159.80
7 purchase totals =	$1,006.41		$1,080.3088	$1,080.30	$1,080.35	$1,080.20