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	$191.82	13.390%	$217.5047	$217.50	$217.50	$217.50
Purchase #2	$32.50	10.249%	$35.8309	$35.83	$35.85	$35.80
Purchase #3	$152.26	4.531%	$159.1589	$159.16	$159.15	$159.20
Purchase #4	$57.89	8.368%	$62.7342	$62.73	$62.75	$62.70
Purchase #5	$96.74	13.358%	$109.6625	$109.66	$109.65	$109.70
Purchase #6	$235.83	5.746%	$249.3808	$249.38	$249.40	$249.40
Purchase #7	$233.35	12.232%	$261.8934	$261.89	$261.90	$261.90
7 purchase totals =	$1,000.39		$1,096.1654	$1,096.15	$1,096.20	$1,096.20