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	$31.99	6.367%	$34.0268	$34.03	$34.05	$34.00
Purchase #2	$148.84	13.466%	$168.8828	$168.88	$168.90	$168.90
Purchase #3	$181.26	5.865%	$191.8909	$191.89	$191.90	$191.90
Purchase #4	$238.61	8.592%	$259.1114	$259.11	$259.10	$259.10
Purchase #5	$116.88	5.449%	$123.2488	$123.25	$123.25	$123.20
Purchase #6	$240.73	3.184%	$248.3948	$248.39	$248.40	$248.40
Purchase #7	$221.50	12.240%	$248.6116	$248.61	$248.60	$248.60
7 purchase totals =	$1,179.81		$1,274.1671	$1,274.16	$1,274.20	$1,274.10