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	$83.82	5.661%	$88.5651	$88.57	$88.55	$88.60
Purchase #2	$246.39	11.491%	$274.7027	$274.70	$274.70	$274.70
Purchase #3	$219.33	8.789%	$238.6069	$238.61	$238.60	$238.60
Purchase #4	$210.95	13.260%	$238.922	$238.92	$238.90	$238.90
Purchase #5	$156.45	7.360%	$167.9647	$167.96	$167.95	$168.00
Purchase #6	$249.31	9.166%	$272.1618	$272.16	$272.15	$272.20
Purchase #7	$42.91	10.670%	$47.4885	$47.49	$47.50	$47.50
7 purchase totals =	$1,209.16		$1,328.4117	$1,328.41	$1,328.35	$1,328.50