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	$80.47	11.273%	$89.5414	$89.54	$89.55	$89.50
Purchase #2	$173.76	3.539%	$179.9094	$179.91	$179.90	$179.90
Purchase #3	$47.90	3.468%	$49.5612	$49.56	$49.55	$49.60
Purchase #4	$188.61	10.458%	$208.3348	$208.33	$208.35	$208.30
Purchase #5	$54.90	4.532%	$57.3881	$57.39	$57.40	$57.40
Purchase #6	$112.27	13.648%	$127.5926	$127.59	$127.60	$127.60
Purchase #7	$167.48	4.703%	$175.3566	$175.36	$175.35	$175.40
7 purchase totals =	$825.39		$887.6841	$887.68	$887.70	$887.70