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	$19.76	3.808%	$20.5125	$20.51	$20.50	$20.50
Purchase #2	$78.87	3.213%	$81.4041	$81.40	$81.40	$81.40
Purchase #3	$224.81	6.287%	$238.9438	$238.94	$238.95	$238.90
Purchase #4	$131.82	12.378%	$148.1367	$148.14	$148.15	$148.10
Purchase #5	$144.87	8.289%	$156.8783	$156.88	$156.90	$156.90
Purchase #6	$247.79	12.775%	$279.4452	$279.45	$279.45	$279.40
Purchase #7	$216.91	12.567%	$244.1691	$244.17	$244.15	$244.20
7 purchase totals =	$1,064.83		$1,169.4897	$1,169.49	$1,169.50	$1,169.40