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	$90.61	5.841%	$95.9025	$95.90	$95.90	$95.90
Purchase #2	$103.66	9.630%	$113.6425	$113.64	$113.65	$113.60
Purchase #3	$217.55	7.471%	$233.8032	$233.80	$233.80	$233.80
Purchase #4	$109.30	11.650%	$122.0335	$122.03	$122.05	$122.00
Purchase #5	$36.42	5.405%	$38.3885	$38.39	$38.40	$38.40
Purchase #6	$80.51	11.474%	$89.7477	$89.75	$89.75	$89.70
Purchase #7	$99.65	9.680%	$109.2961	$109.30	$109.30	$109.30
7 purchase totals =	$737.70		$802.8140	$802.81	$802.85	$802.70