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	$96.25	4.786%	$100.8565	$100.86	$100.85	$100.90
Purchase #2	$121.69	11.639%	$135.8535	$135.85	$135.85	$135.90
Purchase #3	$86.86	4.300%	$90.595	$90.60	$90.60	$90.60
Purchase #4	$53.67	8.824%	$58.4058	$58.41	$58.40	$58.40
Purchase #5	$91.84	13.515%	$104.2522	$104.25	$104.25	$104.30
Purchase #6	$25.53	12.282%	$28.6656	$28.67	$28.65	$28.70
Purchase #7	$20.52	5.439%	$21.6361	$21.64	$21.65	$21.60
7 purchase totals =	$496.36		$540.2647	$540.28	$540.25	$540.40