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	$217.77	7.873%	$234.915	$234.92	$234.90	$234.90
Purchase #2	$232.90	3.142%	$240.2177	$240.22	$240.20	$240.20
Purchase #3	$66.55	8.844%	$72.4357	$72.44	$72.45	$72.40
Purchase #4	$120.69	6.338%	$128.3393	$128.34	$128.35	$128.30
Purchase #5	$75.93	9.207%	$82.9209	$82.92	$82.90	$82.90
Purchase #6	$92.50	13.664%	$105.1392	$105.14	$105.15	$105.10
Purchase #7	$30.85	5.323%	$32.4921	$32.49	$32.50	$32.50
7 purchase totals =	$837.19		$896.4599	$896.47	$896.45	$896.30