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	$116.97	5.501%	$123.4045	$123.40	$123.40	$123.40
Purchase #2	$226.83	10.469%	$250.5768	$250.58	$250.60	$250.60
Purchase #3	$246.55	9.752%	$270.5936	$270.59	$270.60	$270.60
Purchase #4	$11.84	12.402%	$13.3084	$13.31	$13.30	$13.30
Purchase #5	$159.93	4.447%	$167.0421	$167.04	$167.05	$167.00
Purchase #6	$65.69	8.328%	$71.1607	$71.16	$71.15	$71.20
Purchase #7	$86.78	8.793%	$94.4106	$94.41	$94.40	$94.40
7 purchase totals =	$914.59		$990.4967	$990.49	$990.50	$990.50