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	$175.75	4.259%	$183.2352	$183.24	$183.25	$183.20
Purchase #2	$181.58	3.436%	$187.8191	$187.82	$187.80	$187.80
Purchase #3	$133.64	3.456%	$138.2586	$138.26	$138.25	$138.30
Purchase #4	$82.47	9.539%	$90.3368	$90.34	$90.35	$90.30
Purchase #5	$196.78	10.152%	$216.7571	$216.76	$216.75	$216.80
Purchase #6	$124.27	6.836%	$132.7651	$132.77	$132.75	$132.80
Purchase #7	$195.58	10.172%	$215.4744	$215.47	$215.45	$215.50
7 purchase totals =	$1,090.07		$1,164.6463	$1,164.66	$1,164.60	$1,164.70