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	$124.88	12.764%	$140.8197	$140.82	$140.80	$140.80
Purchase #2	$193.45	11.762%	$216.2036	$216.20	$216.20	$216.20
Purchase #3	$118.36	7.669%	$127.437	$127.44	$127.45	$127.40
Purchase #4	$172.78	13.652%	$196.3679	$196.37	$196.35	$196.40
Purchase #5	$64.69	8.839%	$70.4079	$70.41	$70.40	$70.40
Purchase #6	$83.48	5.125%	$87.7584	$87.76	$87.75	$87.80
Purchase #7	$85.39	5.667%	$90.2291	$90.23	$90.25	$90.20
7 purchase totals =	$843.03		$929.2236	$929.23	$929.20	$929.20