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	$117.27	12.409%	$131.822	$131.82	$131.80	$131.80
Purchase #2	$160.63	4.833%	$168.3932	$168.39	$168.40	$168.40
Purchase #3	$33.46	12.297%	$37.5746	$37.57	$37.55	$37.60
Purchase #4	$248.27	3.435%	$256.7981	$256.80	$256.80	$256.80
Purchase #5	$226.98	6.135%	$240.9052	$240.91	$240.90	$240.90
Purchase #6	$128.80	7.514%	$138.478	$138.48	$138.50	$138.50
Purchase #7	$27.65	10.557%	$30.569	$30.57	$30.55	$30.60
7 purchase totals =	$943.06		$1,004.5401	$1,004.54	$1,004.50	$1,004.60