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	$21.57	13.261%	$24.4304	$24.43	$24.45	$24.40
Purchase #2	$89.61	11.557%	$99.9662	$99.97	$99.95	$100.00
Purchase #3	$10.68	5.417%	$11.2585	$11.26	$11.25	$11.30
Purchase #4	$73.43	13.610%	$83.4238	$83.42	$83.40	$83.40
Purchase #5	$85.29	4.300%	$88.9575	$88.96	$88.95	$89.00
Purchase #6	$232.44	9.843%	$255.3191	$255.32	$255.30	$255.30
Purchase #7	$99.83	4.610%	$104.4322	$104.43	$104.45	$104.40
7 purchase totals =	$612.85		$667.7877	$667.79	$667.75	$667.80