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	$37.36	5.783%	$39.5205	$39.52	$39.50	$39.50
Purchase #2	$241.61	9.390%	$264.2972	$264.30	$264.30	$264.30
Purchase #3	$63.66	12.693%	$71.7404	$71.74	$71.75	$71.70
Purchase #4	$55.89	10.210%	$61.5964	$61.60	$61.60	$61.60
Purchase #5	$81.35	7.265%	$87.2601	$87.26	$87.25	$87.30
Purchase #6	$127.83	13.347%	$144.8915	$144.89	$144.90	$144.90
Purchase #7	$215.46	13.707%	$244.9931	$244.99	$245.00	$245.00
7 purchase totals =	$823.16		$914.2992	$914.30	$914.30	$914.30