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	$75.87	3.371%	$78.4276	$78.43	$78.45	$78.40
Purchase #2	$93.48	6.208%	$99.2832	$99.28	$99.30	$99.30
Purchase #3	$205.82	7.202%	$220.6432	$220.64	$220.65	$220.60
Purchase #4	$155.35	5.603%	$164.0543	$164.05	$164.05	$164.10
Purchase #5	$36.45	11.534%	$40.6541	$40.65	$40.65	$40.70
Purchase #6	$84.72	7.187%	$90.8088	$90.81	$90.80	$90.80
Purchase #7	$198.69	8.308%	$215.1972	$215.20	$215.20	$215.20
7 purchase totals =	$850.38		$909.0684	$909.06	$909.10	$909.10