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	$85.95	5.417%	$90.6059	$90.61	$90.60	$90.60
Purchase #2	$236.72	10.726%	$262.1106	$262.11	$262.10	$262.10
Purchase #3	$144.68	13.425%	$164.1033	$164.10	$164.10	$164.10
Purchase #4	$234.32	13.270%	$265.4143	$265.41	$265.40	$265.40
Purchase #5	$89.35	13.222%	$101.1639	$101.16	$101.15	$101.20
Purchase #6	$44.84	9.279%	$49.0007	$49.00	$49.00	$49.00
Purchase #7	$102.29	6.509%	$108.9481	$108.95	$108.95	$108.90
7 purchase totals =	$938.15		$1,041.3468	$1,041.34	$1,041.30	$1,041.30