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	$50.72	11.386%	$56.495	$56.50	$56.50	$56.50
Purchase #2	$219.76	13.181%	$248.7266	$248.73	$248.75	$248.70
Purchase #3	$122.49	3.795%	$127.1385	$127.14	$127.15	$127.10
Purchase #4	$123.93	6.813%	$132.3734	$132.37	$132.35	$132.40
Purchase #5	$150.98	11.502%	$168.3457	$168.35	$168.35	$168.30
Purchase #6	$237.38	8.462%	$257.4671	$257.47	$257.45	$257.50
Purchase #7	$169.79	11.175%	$188.764	$188.76	$188.75	$188.80
7 purchase totals =	$1,075.05		$1,179.3103	$1,179.32	$1,179.30	$1,179.30