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	$52.27	3.375%	$54.0341	$54.03	$54.05	$54.00
Purchase #2	$23.49	5.786%	$24.8491	$24.85	$24.85	$24.80
Purchase #3	$85.95	4.217%	$89.5745	$89.57	$89.55	$89.60
Purchase #4	$148.72	12.522%	$167.3427	$167.34	$167.35	$167.30
Purchase #5	$50.33	8.400%	$54.5577	$54.56	$54.55	$54.60
Purchase #6	$233.70	12.346%	$262.5526	$262.55	$262.55	$262.60
Purchase #7	$168.79	10.130%	$185.8884	$185.89	$185.90	$185.90
7 purchase totals =	$763.25		$838.7991	$838.79	$838.80	$838.80