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	$142.67	6.174%	$151.4784	$151.48	$151.50	$151.50
Purchase #2	$54.56	13.873%	$62.1291	$62.13	$62.15	$62.10
Purchase #3	$161.63	11.660%	$180.4761	$180.48	$180.50	$180.50
Purchase #4	$198.34	7.455%	$213.1262	$213.13	$213.15	$213.10
Purchase #5	$87.49	12.673%	$98.5776	$98.58	$98.60	$98.60
Purchase #6	$218.87	8.436%	$237.3339	$237.33	$237.35	$237.30
Purchase #7	$129.72	11.219%	$144.2733	$144.27	$144.25	$144.30
7 purchase totals =	$993.28		$1,087.3946	$1,087.40	$1,087.50	$1,087.40