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	$73.30	12.706%	$82.6135	$82.61	$82.60	$82.60
Purchase #2	$103.96	4.129%	$108.2525	$108.25	$108.25	$108.30
Purchase #3	$83.41	13.234%	$94.4485	$94.45	$94.45	$94.40
Purchase #4	$161.83	10.257%	$178.4289	$178.43	$178.45	$178.40
Purchase #5	$38.84	5.693%	$41.0512	$41.05	$41.05	$41.10
Purchase #6	$228.64	7.469%	$245.7171	$245.72	$245.70	$245.70
Purchase #7	$146.96	12.448%	$165.2536	$165.25	$165.25	$165.30
7 purchase totals =	$836.94		$915.7653	$915.76	$915.75	$915.80