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	$23.70	7.342%	$25.4401	$25.44	$25.45	$25.40
Purchase #2	$164.89	8.118%	$178.2758	$178.28	$178.30	$178.30
Purchase #3	$76.36	3.175%	$78.7844	$78.78	$78.80	$78.80
Purchase #4	$158.46	8.865%	$172.5075	$172.51	$172.50	$172.50
Purchase #5	$248.61	4.196%	$259.0417	$259.04	$259.05	$259.00
Purchase #6	$148.95	12.659%	$167.8056	$167.81	$167.80	$167.80
Purchase #7	$86.87	7.333%	$93.2402	$93.24	$93.25	$93.20
7 purchase totals =	$907.84		$975.0953	$975.10	$975.15	$975.00