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	$166.44	12.115%	$186.6042	$186.60	$186.60	$186.60
Purchase #2	$172.34	7.554%	$185.3586	$185.36	$185.35	$185.40
Purchase #3	$98.29	5.228%	$103.4286	$103.43	$103.45	$103.40
Purchase #4	$150.53	11.850%	$168.3678	$168.37	$168.35	$168.40
Purchase #5	$12.79	5.662%	$13.5142	$13.51	$13.50	$13.50
Purchase #6	$133.99	12.282%	$150.4467	$150.45	$150.45	$150.40
Purchase #7	$234.31	6.451%	$249.4253	$249.43	$249.45	$249.40
7 purchase totals =	$968.69		$1,057.1454	$1,057.15	$1,057.15	$1,057.10