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	$32.47	13.621%	$36.8927	$36.89	$36.90	$36.90
Purchase #2	$127.58	6.117%	$135.3841	$135.38	$135.40	$135.40
Purchase #3	$177.64	4.633%	$185.8701	$185.87	$185.85	$185.90
Purchase #4	$29.83	5.498%	$31.4701	$31.47	$31.45	$31.50
Purchase #5	$97.88	13.636%	$111.2269	$111.23	$111.25	$111.20
Purchase #6	$6.41	3.576%	$6.6392	$6.64	$6.65	$6.60
Purchase #7	$85.73	5.811%	$90.7118	$90.71	$90.70	$90.70
7 purchase totals =	$557.54		$598.1949	$598.19	$598.20	$598.20