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	$5.82	4.423%	$6.0774	$6.08	$6.10	$6.10
Purchase #2	$245.50	8.237%	$265.7218	$265.72	$265.70	$265.70
Purchase #3	$36.83	8.867%	$40.0957	$40.10	$40.10	$40.10
Purchase #4	$153.86	11.558%	$171.6431	$171.64	$171.65	$171.60
Purchase #5	$83.87	6.671%	$89.465	$89.47	$89.45	$89.50
Purchase #6	$109.54	7.168%	$117.3918	$117.39	$117.40	$117.40
Purchase #7	$188.75	4.600%	$197.4325	$197.43	$197.45	$197.40
7 purchase totals =	$824.17		$887.8273	$887.83	$887.85	$887.80