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	$74.96	7.442%	$80.5385	$80.54	$80.55	$80.50
Purchase #2	$241.98	13.737%	$275.2208	$275.22	$275.20	$275.20
Purchase #3	$108.79	5.656%	$114.9432	$114.94	$114.95	$114.90
Purchase #4	$195.60	8.549%	$212.3218	$212.32	$212.30	$212.30
Purchase #5	$62.67	13.466%	$71.1091	$71.11	$71.10	$71.10
Purchase #6	$174.40	7.746%	$187.909	$187.91	$187.90	$187.90
Purchase #7	$33.32	9.344%	$36.4334	$36.43	$36.45	$36.40
7 purchase totals =	$891.72		$978.4758	$978.47	$978.45	$978.30