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	$38.72	8.663%	$42.0743	$42.07	$42.05	$42.10
Purchase #2	$163.92	9.759%	$179.917	$179.92	$179.90	$179.90
Purchase #3	$137.51	5.816%	$145.5076	$145.51	$145.50	$145.50
Purchase #4	$221.41	4.526%	$231.431	$231.43	$231.45	$231.40
Purchase #5	$28.87	6.709%	$30.8069	$30.81	$30.80	$30.80
Purchase #6	$124.54	13.725%	$141.6331	$141.63	$141.65	$141.60
Purchase #7	$202.47	13.377%	$229.5544	$229.55	$229.55	$229.60
7 purchase totals =	$917.44		$1,000.9243	$1,000.92	$1,000.90	$1,000.90