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	$126.54	11.872%	$141.5628	$141.56	$141.55	$141.60
Purchase #2	$179.66	9.370%	$196.4941	$196.49	$196.50	$196.50
Purchase #3	$118.89	4.359%	$124.0724	$124.07	$124.05	$124.10
Purchase #4	$81.27	10.732%	$89.9919	$89.99	$90.00	$90.00
Purchase #5	$46.63	4.560%	$48.7563	$48.76	$48.75	$48.80
Purchase #6	$192.60	3.474%	$199.2909	$199.29	$199.30	$199.30
Purchase #7	$38.56	10.452%	$42.5903	$42.59	$42.60	$42.60
7 purchase totals =	$784.15		$842.7587	$842.75	$842.75	$842.90