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	$38.74	4.120%	$40.3361	$40.34	$40.35	$40.30
Purchase #2	$41.70	3.195%	$43.0323	$43.03	$43.05	$43.00
Purchase #3	$11.38	13.782%	$12.9484	$12.95	$12.95	$12.90
Purchase #4	$226.44	5.265%	$238.3621	$238.36	$238.35	$238.40
Purchase #5	$42.32	6.855%	$45.221	$45.22	$45.20	$45.20
Purchase #6	$152.93	9.362%	$167.2473	$167.25	$167.25	$167.20
Purchase #7	$152.79	7.794%	$164.6985	$164.70	$164.70	$164.70
7 purchase totals =	$666.30		$711.8457	$711.85	$711.85	$711.70