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	$94.60	5.795%	$100.0821	$100.08	$100.10	$100.10
Purchase #2	$89.88	6.606%	$95.8175	$95.82	$95.80	$95.80
Purchase #3	$164.65	9.525%	$180.3329	$180.33	$180.35	$180.30
Purchase #4	$94.45	7.362%	$101.4034	$101.40	$101.40	$101.40
Purchase #5	$249.79	9.429%	$273.3427	$273.34	$273.35	$273.30
Purchase #6	$11.66	7.205%	$12.5001	$12.50	$12.50	$12.50
Purchase #7	$202.45	12.590%	$227.9385	$227.94	$227.95	$227.90
7 purchase totals =	$907.48		$991.4172	$991.41	$991.45	$991.30