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	$82.48	9.233%	$90.0954	$90.10	$90.10	$90.10
Purchase #2	$195.90	4.826%	$205.3541	$205.35	$205.35	$205.40
Purchase #3	$152.84	10.480%	$168.8576	$168.86	$168.85	$168.90
Purchase #4	$114.79	3.114%	$118.3646	$118.36	$118.35	$118.40
Purchase #5	$174.64	11.141%	$194.0966	$194.10	$194.10	$194.10
Purchase #6	$241.83	3.407%	$250.0691	$250.07	$250.05	$250.10
Purchase #7	$170.77	10.800%	$189.2132	$189.21	$189.20	$189.20
7 purchase totals =	$1,133.25		$1,216.0506	$1,216.05	$1,216.00	$1,216.20