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	$233.77	11.725%	$261.1795	$261.18	$261.20	$261.20
Purchase #2	$143.37	8.491%	$155.5435	$155.54	$155.55	$155.50
Purchase #3	$15.63	8.278%	$16.9239	$16.92	$16.90	$16.90
Purchase #4	$196.75	11.389%	$219.1579	$219.16	$219.15	$219.20
Purchase #5	$25.57	9.176%	$27.9163	$27.92	$27.90	$27.90
Purchase #6	$37.72	11.470%	$42.0465	$42.05	$42.05	$42.00
Purchase #7	$227.70	13.700%	$258.8949	$258.89	$258.90	$258.90
7 purchase totals =	$880.51		$981.6625	$981.66	$981.65	$981.60