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	$32.56	13.679%	$37.0139	$37.01	$37.00	$37.00
Purchase #2	$246.87	9.658%	$270.7127	$270.71	$270.70	$270.70
Purchase #3	$102.68	9.299%	$112.2282	$112.23	$112.25	$112.20
Purchase #4	$81.54	11.390%	$90.8274	$90.83	$90.85	$90.80
Purchase #5	$141.45	7.800%	$152.4831	$152.48	$152.50	$152.50
Purchase #6	$41.26	11.532%	$46.0181	$46.02	$46.00	$46.00
Purchase #7	$167.93	6.823%	$179.3879	$179.39	$179.40	$179.40
7 purchase totals =	$814.29		$888.6713	$888.67	$888.70	$888.60