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	$27.25	5.728%	$28.8109	$28.81	$28.80	$28.80
Purchase #2	$50.77	7.473%	$54.564	$54.56	$54.55	$54.60
Purchase #3	$137.88	13.457%	$156.4345	$156.43	$156.45	$156.40
Purchase #4	$134.36	8.493%	$145.7712	$145.77	$145.75	$145.80
Purchase #5	$212.41	13.262%	$240.5798	$240.58	$240.60	$240.60
Purchase #6	$160.83	3.124%	$165.8543	$165.85	$165.85	$165.90
Purchase #7	$84.78	3.862%	$88.0542	$88.05	$88.05	$88.10
7 purchase totals =	$808.28		$880.0689	$880.05	$880.05	$880.20