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	$29.40	6.184%	$31.2181	$31.22	$31.20	$31.20
Purchase #2	$36.64	12.208%	$41.113	$41.11	$41.10	$41.10
Purchase #3	$146.31	12.746%	$164.9587	$164.96	$164.95	$165.00
Purchase #4	$45.60	10.539%	$50.4058	$50.41	$50.40	$50.40
Purchase #5	$69.37	11.260%	$77.1811	$77.18	$77.20	$77.20
Purchase #6	$221.69	7.482%	$238.2768	$238.28	$238.30	$238.30
Purchase #7	$150.84	3.561%	$156.2114	$156.21	$156.20	$156.20
7 purchase totals =	$699.85		$759.3649	$759.37	$759.35	$759.40