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	$79.58	4.669%	$83.2956	$83.30	$83.30	$83.30
Purchase #2	$37.93	13.848%	$43.1825	$43.18	$43.20	$43.20
Purchase #3	$114.72	3.208%	$118.4002	$118.40	$118.40	$118.40
Purchase #4	$136.39	3.830%	$141.6137	$141.61	$141.60	$141.60
Purchase #5	$234.68	10.543%	$259.4223	$259.42	$259.40	$259.40
Purchase #6	$167.69	13.178%	$189.7882	$189.79	$189.80	$189.80
Purchase #7	$19.67	11.371%	$21.9067	$21.91	$21.90	$21.90
7 purchase totals =	$790.66		$857.6092	$857.61	$857.60	$857.60