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	$69.55	11.444%	$77.5093	$77.51	$77.50	$77.50
Purchase #2	$108.31	10.719%	$119.9197	$119.92	$119.90	$119.90
Purchase #3	$22.28	5.601%	$23.5279	$23.53	$23.55	$23.50
Purchase #4	$213.74	8.321%	$231.5253	$231.53	$231.55	$231.50
Purchase #5	$118.27	7.738%	$127.4217	$127.42	$127.40	$127.40
Purchase #6	$141.56	10.215%	$156.0204	$156.02	$156.00	$156.00
Purchase #7	$213.90	5.484%	$225.6303	$225.63	$225.65	$225.60
7 purchase totals =	$887.61		$961.5546	$961.56	$961.55	$961.40