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	$226.90	6.500%	$241.6485	$241.65	$241.65	$241.60
Purchase #2	$220.52	9.124%	$240.6402	$240.64	$240.65	$240.60
Purchase #3	$94.87	5.149%	$99.7549	$99.75	$99.75	$99.80
Purchase #4	$37.73	5.644%	$39.8595	$39.86	$39.85	$39.90
Purchase #5	$234.35	11.306%	$260.8456	$260.85	$260.85	$260.80
Purchase #6	$19.31	8.365%	$20.9253	$20.93	$20.95	$20.90
Purchase #7	$167.97	10.608%	$185.7883	$185.79	$185.80	$185.80
7 purchase totals =	$1,001.65		$1,089.4623	$1,089.47	$1,089.50	$1,089.40