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	$90.75	10.440%	$100.2243	$100.22	$100.20	$100.20
Purchase #2	$140.58	7.804%	$151.5509	$151.55	$151.55	$151.60
Purchase #3	$31.59	12.693%	$35.5997	$35.60	$35.60	$35.60
Purchase #4	$152.81	4.429%	$159.578	$159.58	$159.60	$159.60
Purchase #5	$195.64	5.362%	$206.1302	$206.13	$206.15	$206.10
Purchase #6	$215.40	8.407%	$233.5087	$233.51	$233.50	$233.50
Purchase #7	$53.64	5.586%	$56.6363	$56.64	$56.65	$56.60
7 purchase totals =	$880.41		$943.2281	$943.23	$943.25	$943.20