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	$160.96	11.576%	$179.5927	$179.59	$179.60	$179.60
Purchase #2	$111.66	11.423%	$124.4149	$124.41	$124.40	$124.40
Purchase #3	$31.51	7.175%	$33.7708	$33.77	$33.75	$33.80
Purchase #4	$128.72	6.825%	$137.5051	$137.51	$137.50	$137.50
Purchase #5	$188.56	5.541%	$199.0081	$199.01	$199.00	$199.00
Purchase #6	$127.57	4.712%	$133.5811	$133.58	$133.60	$133.60
Purchase #7	$73.87	4.260%	$77.0169	$77.02	$77.00	$77.00
7 purchase totals =	$822.85		$884.8896	$884.89	$884.85	$884.90