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	$78.46	13.553%	$89.0937	$89.09	$89.10	$89.10
Purchase #2	$56.94	3.376%	$58.8623	$58.86	$58.85	$58.90
Purchase #3	$31.43	6.602%	$33.505	$33.51	$33.50	$33.50
Purchase #4	$248.85	9.309%	$272.0154	$272.02	$272.00	$272.00
Purchase #5	$25.70	9.364%	$28.1065	$28.11	$28.10	$28.10
Purchase #6	$226.59	3.105%	$233.6256	$233.63	$233.65	$233.60
Purchase #7	$25.96	5.352%	$27.3494	$27.35	$27.35	$27.30
7 purchase totals =	$693.93		$742.5579	$742.57	$742.55	$742.50