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	$70.90	3.293%	$73.2347	$73.23	$73.25	$73.20
Purchase #2	$126.75	12.775%	$142.9423	$142.94	$142.95	$142.90
Purchase #3	$37.83	12.723%	$42.6431	$42.64	$42.65	$42.60
Purchase #4	$5.83	4.458%	$6.0899	$6.09	$6.10	$6.10
Purchase #5	$123.35	10.719%	$136.5719	$136.57	$136.55	$136.60
Purchase #6	$249.52	9.211%	$272.5033	$272.50	$272.50	$272.50
Purchase #7	$126.38	12.719%	$142.4543	$142.45	$142.45	$142.50
7 purchase totals =	$740.56		$816.4395	$816.42	$816.45	$816.40