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	$83.86	6.534%	$89.3394	$89.34	$89.35	$89.30
Purchase #2	$35.68	13.169%	$40.3787	$40.38	$40.40	$40.40
Purchase #3	$217.44	5.440%	$229.2687	$229.27	$229.25	$229.30
Purchase #4	$199.94	12.635%	$225.2024	$225.20	$225.20	$225.20
Purchase #5	$134.59	11.654%	$150.2751	$150.28	$150.30	$150.30
Purchase #6	$217.42	5.342%	$229.0346	$229.03	$229.05	$229.00
Purchase #7	$210.49	12.390%	$236.5697	$236.57	$236.55	$236.60
7 purchase totals =	$1,099.42		$1,200.0686	$1,200.07	$1,200.10	$1,200.10