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	$117.48	11.740%	$131.2722	$131.27	$131.25	$131.30
Purchase #2	$59.84	8.517%	$64.9366	$64.94	$64.95	$64.90
Purchase #3	$145.49	12.821%	$164.1433	$164.14	$164.15	$164.10
Purchase #4	$243.72	8.265%	$263.8635	$263.86	$263.85	$263.90
Purchase #5	$234.62	6.488%	$249.8421	$249.84	$249.85	$249.80
Purchase #6	$108.77	12.484%	$122.3488	$122.35	$122.35	$122.30
Purchase #7	$103.64	8.704%	$112.6608	$112.66	$112.65	$112.70
7 purchase totals =	$1,013.56		$1,109.0673	$1,109.06	$1,109.05	$1,109.00