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	$97.74	6.555%	$104.1469	$104.15	$104.15	$104.10
Purchase #2	$168.74	7.824%	$181.9422	$181.94	$181.95	$181.90
Purchase #3	$51.49	5.387%	$54.2638	$54.26	$54.25	$54.30
Purchase #4	$176.41	11.368%	$196.4643	$196.46	$196.45	$196.50
Purchase #5	$21.48	13.608%	$24.403	$24.40	$24.40	$24.40
Purchase #6	$162.77	12.380%	$182.9209	$182.92	$182.90	$182.90
Purchase #7	$234.86	8.192%	$254.0997	$254.10	$254.10	$254.10
7 purchase totals =	$913.49		$998.2408	$998.23	$998.20	$998.20