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	$55.91	5.397%	$58.9275	$58.93	$58.95	$58.90
Purchase #2	$96.88	7.182%	$103.8379	$103.84	$103.85	$103.80
Purchase #3	$19.73	3.413%	$20.4034	$20.40	$20.40	$20.40
Purchase #4	$10.79	7.376%	$11.5859	$11.59	$11.60	$11.60
Purchase #5	$198.34	12.192%	$222.5216	$222.52	$222.50	$222.50
Purchase #6	$151.41	13.740%	$172.2137	$172.21	$172.20	$172.20
Purchase #7	$170.78	8.601%	$185.4688	$185.47	$185.45	$185.50
7 purchase totals =	$703.84		$774.9588	$774.96	$774.95	$774.90