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	$38.50	9.269%	$42.0686	$42.07	$42.05	$42.10
Purchase #2	$74.32	7.509%	$79.9007	$79.90	$79.90	$79.90
Purchase #3	$18.79	11.182%	$20.8911	$20.89	$20.90	$20.90
Purchase #4	$22.89	7.401%	$24.5841	$24.58	$24.60	$24.60
Purchase #5	$138.75	12.807%	$156.5197	$156.52	$156.50	$156.50
Purchase #6	$120.40	11.256%	$133.9522	$133.95	$133.95	$134.00
Purchase #7	$64.77	3.774%	$67.2144	$67.21	$67.20	$67.20
7 purchase totals =	$478.42		$525.1308	$525.12	$525.10	$525.20