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	$134.48	8.479%	$145.8826	$145.88	$145.90	$145.90
Purchase #2	$227.41	9.516%	$249.0503	$249.05	$249.05	$249.10
Purchase #3	$59.88	12.369%	$67.2866	$67.29	$67.30	$67.30
Purchase #4	$134.61	5.379%	$141.8507	$141.85	$141.85	$141.90
Purchase #5	$82.52	12.404%	$92.7558	$92.76	$92.75	$92.80
Purchase #6	$21.59	9.403%	$23.6201	$23.62	$23.60	$23.60
Purchase #7	$137.81	4.435%	$143.9219	$143.92	$143.90	$143.90
7 purchase totals =	$798.30		$864.3680	$864.37	$864.35	$864.50