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	$192.87	12.300%	$216.593	$216.59	$216.60	$216.60
Purchase #2	$99.85	7.579%	$107.4176	$107.42	$107.40	$107.40
Purchase #3	$16.65	11.382%	$18.5451	$18.55	$18.55	$18.50
Purchase #4	$177.78	12.665%	$200.2958	$200.30	$200.30	$200.30
Purchase #5	$243.58	10.376%	$268.8539	$268.85	$268.85	$268.90
Purchase #6	$165.59	9.191%	$180.8094	$180.81	$180.80	$180.80
Purchase #7	$53.54	10.772%	$59.3073	$59.31	$59.30	$59.30
7 purchase totals =	$949.86		$1,051.8221	$1,051.83	$1,051.80	$1,051.80