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	$19.67	9.543%	$21.5471	$21.55	$21.55	$21.50
Purchase #2	$84.88	7.187%	$90.9803	$90.98	$91.00	$91.00
Purchase #3	$119.63	6.286%	$127.1499	$127.15	$127.15	$127.10
Purchase #4	$54.43	4.748%	$57.0143	$57.01	$57.00	$57.00
Purchase #5	$91.98	8.864%	$100.1331	$100.13	$100.15	$100.10
Purchase #6	$81.63	12.622%	$91.9333	$91.93	$91.95	$91.90
Purchase #7	$122.32	9.234%	$133.615	$133.62	$133.60	$133.60
7 purchase totals =	$574.54		$622.3730	$622.37	$622.40	$622.20