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	$60.49	3.160%	$62.4015	$62.40	$62.40	$62.40
Purchase #2	$229.56	13.170%	$259.7931	$259.79	$259.80	$259.80
Purchase #3	$51.38	6.840%	$54.8944	$54.89	$54.90	$54.90
Purchase #4	$227.34	9.530%	$249.0055	$249.01	$249.00	$249.00
Purchase #5	$85.42	4.168%	$88.9803	$88.98	$89.00	$89.00
Purchase #6	$136.39	5.394%	$143.7469	$143.75	$143.75	$143.70
Purchase #7	$34.46	11.682%	$38.4856	$38.49	$38.50	$38.50
7 purchase totals =	$825.04		$897.3073	$897.31	$897.35	$897.30