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	$86.78	5.389%	$91.4566	$91.46	$91.45	$91.50
Purchase #2	$148.71	12.259%	$166.9404	$166.94	$166.95	$166.90
Purchase #3	$104.32	7.373%	$112.0115	$112.01	$112.00	$112.00
Purchase #4	$194.47	11.323%	$216.4898	$216.49	$216.50	$216.50
Purchase #5	$138.33	8.233%	$149.7187	$149.72	$149.70	$149.70
Purchase #6	$70.37	3.308%	$72.6978	$72.70	$72.70	$72.70
Purchase #7	$146.42	10.798%	$162.2304	$162.23	$162.25	$162.20
7 purchase totals =	$889.40		$971.5452	$971.55	$971.55	$971.50