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	$218.70	13.776%	$248.8281	$248.83	$248.85	$248.80
Purchase #2	$65.95	10.223%	$72.6921	$72.69	$72.70	$72.70
Purchase #3	$41.91	3.237%	$43.2666	$43.27	$43.25	$43.30
Purchase #4	$116.29	13.462%	$131.945	$131.95	$131.95	$131.90
Purchase #5	$128.95	6.555%	$137.4027	$137.40	$137.40	$137.40
Purchase #6	$147.28	3.504%	$152.4407	$152.44	$152.45	$152.40
Purchase #7	$41.58	6.840%	$44.4241	$44.42	$44.40	$44.40
7 purchase totals =	$760.66		$830.9993	$831.00	$831.00	$830.90