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	$232.95	9.691%	$255.5252	$255.53	$255.55	$255.50
Purchase #2	$69.52	13.384%	$78.8246	$78.82	$78.80	$78.80
Purchase #3	$11.65	5.695%	$12.3135	$12.31	$12.30	$12.30
Purchase #4	$172.72	6.410%	$183.7914	$183.79	$183.80	$183.80
Purchase #5	$117.66	11.477%	$131.1638	$131.16	$131.15	$131.20
Purchase #6	$16.40	4.803%	$17.1877	$17.19	$17.20	$17.20
Purchase #7	$136.76	8.809%	$148.8072	$148.81	$148.80	$148.80
7 purchase totals =	$757.66		$827.6134	$827.61	$827.60	$827.60