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	$75.63	8.306%	$81.9118	$81.91	$81.90	$81.90
Purchase #2	$102.94	13.522%	$116.8595	$116.86	$116.85	$116.90
Purchase #3	$154.65	3.808%	$160.5391	$160.54	$160.55	$160.50
Purchase #4	$214.39	9.404%	$234.5512	$234.55	$234.55	$234.60
Purchase #5	$79.60	12.620%	$89.6455	$89.65	$89.65	$89.60
Purchase #6	$116.63	11.275%	$129.78	$129.78	$129.80	$129.80
Purchase #7	$157.56	13.765%	$179.2481	$179.25	$179.25	$179.20
7 purchase totals =	$901.40		$992.5352	$992.54	$992.55	$992.50