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	$51.34	11.739%	$57.3668	$57.37	$57.35	$57.40
Purchase #2	$244.88	12.205%	$274.7676	$274.77	$274.75	$274.80
Purchase #3	$87.97	3.330%	$90.8994	$90.90	$90.90	$90.90
Purchase #4	$135.71	7.162%	$145.4296	$145.43	$145.45	$145.40
Purchase #5	$249.44	9.382%	$272.8425	$272.84	$272.85	$272.80
Purchase #6	$206.82	8.826%	$225.0739	$225.07	$225.05	$225.10
Purchase #7	$98.79	7.792%	$106.4877	$106.49	$106.50	$106.50
7 purchase totals =	$1,074.95		$1,172.8675	$1,172.87	$1,172.85	$1,172.90