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	$238.89	13.619%	$271.4244	$271.42	$271.40	$271.40
Purchase #2	$65.32	10.219%	$71.9951	$72.00	$72.00	$72.00
Purchase #3	$94.86	8.696%	$103.109	$103.11	$103.10	$103.10
Purchase #4	$102.88	6.123%	$109.1793	$109.18	$109.20	$109.20
Purchase #5	$139.53	12.369%	$156.7885	$156.79	$156.80	$156.80
Purchase #6	$238.44	7.161%	$255.5147	$255.51	$255.50	$255.50
Purchase #7	$11.74	6.488%	$12.5017	$12.50	$12.50	$12.50
7 purchase totals =	$891.66		$980.5127	$980.51	$980.50	$980.50