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	$91.90	12.579%	$103.4601	$103.46	$103.45	$103.50
Purchase #2	$37.98	4.335%	$39.6264	$39.63	$39.65	$39.60
Purchase #3	$119.31	3.771%	$123.8092	$123.81	$123.80	$123.80
Purchase #4	$20.31	11.645%	$22.6751	$22.68	$22.70	$22.70
Purchase #5	$59.41	10.227%	$65.4859	$65.49	$65.50	$65.50
Purchase #6	$152.95	12.590%	$172.2064	$172.21	$172.20	$172.20
Purchase #7	$71.53	9.611%	$78.4047	$78.40	$78.40	$78.40
7 purchase totals =	$553.39		$605.6678	$605.68	$605.70	$605.70