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	$6.79	5.627%	$7.1721	$7.17	$7.15	$7.20
Purchase #2	$62.83	13.471%	$71.2938	$71.29	$71.30	$71.30
Purchase #3	$235.43	3.371%	$243.3663	$243.37	$243.35	$243.40
Purchase #4	$69.51	5.285%	$73.1836	$73.18	$73.20	$73.20
Purchase #5	$236.94	12.613%	$266.8252	$266.83	$266.85	$266.80
Purchase #6	$200.35	6.361%	$213.0943	$213.09	$213.10	$213.10
Purchase #7	$80.31	11.104%	$89.2276	$89.23	$89.25	$89.20
7 purchase totals =	$892.16		$964.1629	$964.16	$964.20	$964.20