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	$17.76	5.764%	$18.7837	$18.78	$18.80	$18.80
Purchase #2	$43.57	6.684%	$46.4822	$46.48	$46.50	$46.50
Purchase #3	$62.58	8.497%	$67.8974	$67.90	$67.90	$67.90
Purchase #4	$73.71	10.610%	$81.5306	$81.53	$81.55	$81.50
Purchase #5	$142.32	3.443%	$147.2201	$147.22	$147.20	$147.20
Purchase #6	$105.31	6.582%	$112.2415	$112.24	$112.25	$112.20
Purchase #7	$126.28	9.198%	$137.8952	$137.90	$137.90	$137.90
7 purchase totals =	$571.53		$612.0507	$612.05	$612.10	$612.00