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	$183.30	4.343%	$191.2607	$191.26	$191.25	$191.30
Purchase #2	$29.68	13.256%	$33.6144	$33.61	$33.60	$33.60
Purchase #3	$221.75	12.406%	$249.2603	$249.26	$249.25	$249.30
Purchase #4	$169.35	8.243%	$183.3095	$183.31	$183.30	$183.30
Purchase #5	$53.96	10.374%	$59.5578	$59.56	$59.55	$59.60
Purchase #6	$50.95	13.583%	$57.8705	$57.87	$57.85	$57.90
Purchase #7	$114.37	9.772%	$125.5462	$125.55	$125.55	$125.50
7 purchase totals =	$823.36		$900.4194	$900.42	$900.35	$900.50