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	$82.80	7.857%	$89.3056	$89.31	$89.30	$89.30
Purchase #2	$101.81	11.360%	$113.3756	$113.38	$113.40	$113.40
Purchase #3	$107.40	10.710%	$118.9025	$118.90	$118.90	$118.90
Purchase #4	$243.36	12.775%	$274.4492	$274.45	$274.45	$274.40
Purchase #5	$166.76	8.360%	$180.7011	$180.70	$180.70	$180.70
Purchase #6	$153.25	7.637%	$164.9537	$164.95	$164.95	$165.00
Purchase #7	$43.40	13.358%	$49.1974	$49.20	$49.20	$49.20
7 purchase totals =	$898.78		$990.8851	$990.89	$990.90	$990.90