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	$242.85	6.165%	$257.8217	$257.82	$257.80	$257.80
Purchase #2	$182.26	13.525%	$206.9107	$206.91	$206.90	$206.90
Purchase #3	$38.52	5.171%	$40.5119	$40.51	$40.50	$40.50
Purchase #4	$133.82	11.550%	$149.2762	$149.28	$149.30	$149.30
Purchase #5	$198.28	12.149%	$222.369	$222.37	$222.35	$222.40
Purchase #6	$48.76	12.120%	$54.6697	$54.67	$54.65	$54.70
Purchase #7	$61.66	10.219%	$67.961	$67.96	$67.95	$68.00
7 purchase totals =	$906.15		$999.5202	$999.52	$999.45	$999.60