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	$24.65	13.401%	$27.9533	$27.95	$27.95	$28.00
Purchase #2	$56.89	10.474%	$62.8487	$62.85	$62.85	$62.80
Purchase #3	$37.92	12.270%	$42.5728	$42.57	$42.55	$42.60
Purchase #4	$92.95	13.788%	$105.7659	$105.77	$105.75	$105.80
Purchase #5	$13.26	10.771%	$14.6882	$14.69	$14.70	$14.70
Purchase #6	$36.77	4.777%	$38.5265	$38.53	$38.55	$38.50
Purchase #7	$179.60	11.595%	$200.4246	$200.42	$200.40	$200.40
7 purchase totals =	$442.04		$492.7800	$492.78	$492.75	$492.80