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	$226.42	10.368%	$249.8952	$249.90	$249.90	$249.90
Purchase #2	$175.56	8.142%	$189.8541	$189.85	$189.85	$189.90
Purchase #3	$18.45	5.304%	$19.4286	$19.43	$19.45	$19.40
Purchase #4	$58.51	10.488%	$64.6465	$64.65	$64.65	$64.60
Purchase #5	$87.47	9.274%	$95.582	$95.58	$95.60	$95.60
Purchase #6	$72.65	11.352%	$80.8972	$80.90	$80.90	$80.90
Purchase #7	$187.75	6.422%	$199.8073	$199.81	$199.80	$199.80
7 purchase totals =	$826.81		$900.1109	$900.12	$900.15	$900.10