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	$25.37	10.133%	$27.9407	$27.94	$27.95	$27.90
Purchase #2	$98.48	12.740%	$111.0264	$111.03	$111.05	$111.00
Purchase #3	$43.36	5.778%	$45.8653	$45.87	$45.85	$45.90
Purchase #4	$159.60	4.807%	$167.272	$167.27	$167.25	$167.30
Purchase #5	$190.27	8.776%	$206.9681	$206.97	$206.95	$207.00
Purchase #6	$186.36	3.484%	$192.8528	$192.85	$192.85	$192.90
Purchase #7	$114.68	12.294%	$128.7788	$128.78	$128.80	$128.80
7 purchase totals =	$818.12		$880.7041	$880.71	$880.70	$880.80