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	$71.91	9.226%	$78.5444	$78.54	$78.55	$78.50
Purchase #2	$186.58	7.370%	$200.3309	$200.33	$200.35	$200.30
Purchase #3	$114.52	11.493%	$127.6818	$127.68	$127.70	$127.70
Purchase #4	$102.47	11.716%	$114.4754	$114.48	$114.50	$114.50
Purchase #5	$185.41	3.754%	$192.3703	$192.37	$192.35	$192.40
Purchase #6	$89.47	12.386%	$100.5518	$100.55	$100.55	$100.60
Purchase #7	$133.98	7.779%	$144.4023	$144.40	$144.40	$144.40
7 purchase totals =	$884.34		$958.3569	$958.35	$958.40	$958.40