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	$225.47	10.829%	$249.8861	$249.89	$249.90	$249.90
Purchase #2	$133.78	4.698%	$140.065	$140.07	$140.05	$140.10
Purchase #3	$233.45	5.811%	$247.0158	$247.02	$247.00	$247.00
Purchase #4	$128.93	10.750%	$142.79	$142.79	$142.80	$142.80
Purchase #5	$31.49	12.149%	$35.3157	$35.32	$35.30	$35.30
Purchase #6	$143.89	11.550%	$160.5093	$160.51	$160.50	$160.50
Purchase #7	$52.55	3.786%	$54.5395	$54.54	$54.55	$54.50
7 purchase totals =	$949.56		$1,030.1214	$1,030.14	$1,030.10	$1,030.10