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	$222.65	12.146%	$249.6931	$249.69	$249.70	$249.70
Purchase #2	$105.79	11.442%	$117.8945	$117.89	$117.90	$117.90
Purchase #3	$7.42	9.398%	$8.1173	$8.12	$8.10	$8.10
Purchase #4	$35.29	5.608%	$37.2691	$37.27	$37.25	$37.30
Purchase #5	$164.42	9.248%	$179.6256	$179.63	$179.65	$179.60
Purchase #6	$82.41	9.586%	$90.3098	$90.31	$90.30	$90.30
Purchase #7	$205.90	9.382%	$225.2175	$225.22	$225.20	$225.20
7 purchase totals =	$823.88		$908.1269	$908.13	$908.10	$908.10