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	$104.99	12.693%	$118.3164	$118.32	$118.30	$118.30
Purchase #2	$9.89	8.860%	$10.7663	$10.77	$10.75	$10.80
Purchase #3	$81.50	6.241%	$86.5864	$86.59	$86.60	$86.60
Purchase #4	$50.70	5.357%	$53.416	$53.42	$53.40	$53.40
Purchase #5	$124.50	12.171%	$139.6529	$139.65	$139.65	$139.70
Purchase #6	$80.58	3.138%	$83.1086	$83.11	$83.10	$83.10
Purchase #7	$138.31	3.736%	$143.4773	$143.48	$143.50	$143.50
7 purchase totals =	$590.47		$635.3239	$635.34	$635.30	$635.40