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	$137.91	10.413%	$152.2706	$152.27	$152.25	$152.30
Purchase #2	$43.58	11.660%	$48.6614	$48.66	$48.65	$48.70
Purchase #3	$178.46	6.524%	$190.1027	$190.10	$190.10	$190.10
Purchase #4	$41.92	7.166%	$44.924	$44.92	$44.90	$44.90
Purchase #5	$138.65	9.129%	$151.3074	$151.31	$151.30	$151.30
Purchase #6	$101.82	3.661%	$105.5476	$105.55	$105.55	$105.50
Purchase #7	$206.39	4.389%	$215.4485	$215.45	$215.45	$215.40
7 purchase totals =	$848.73		$908.2622	$908.26	$908.20	$908.20