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	$92.59	6.212%	$98.3417	$98.34	$98.35	$98.30
Purchase #2	$94.75	9.250%	$103.5144	$103.51	$103.50	$103.50
Purchase #3	$14.61	11.630%	$16.3091	$16.31	$16.30	$16.30
Purchase #4	$105.53	5.580%	$111.4186	$111.42	$111.40	$111.40
Purchase #5	$234.44	10.828%	$259.8252	$259.83	$259.85	$259.80
Purchase #6	$208.38	9.102%	$227.3467	$227.35	$227.35	$227.30
Purchase #7	$118.64	4.700%	$124.2161	$124.22	$124.20	$124.20
7 purchase totals =	$868.94		$940.9718	$940.98	$940.95	$940.80