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	$171.53	4.399%	$179.0756	$179.08	$179.10	$179.10
Purchase #2	$60.79	12.524%	$68.4033	$68.40	$68.40	$68.40
Purchase #3	$87.34	13.763%	$99.3606	$99.36	$99.35	$99.40
Purchase #4	$66.98	9.694%	$73.473	$73.47	$73.45	$73.50
Purchase #5	$226.29	12.855%	$255.3796	$255.38	$255.40	$255.40
Purchase #6	$32.85	13.783%	$37.3777	$37.38	$37.40	$37.40
Purchase #7	$103.91	8.623%	$112.8702	$112.87	$112.85	$112.90
7 purchase totals =	$749.69		$825.9400	$825.94	$825.95	$826.10