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	$86.47	4.553%	$90.407	$90.41	$90.40	$90.40
Purchase #2	$147.25	11.531%	$164.2294	$164.23	$164.25	$164.20
Purchase #3	$127.68	7.268%	$136.9598	$136.96	$136.95	$137.00
Purchase #4	$118.81	7.161%	$127.318	$127.32	$127.30	$127.30
Purchase #5	$218.87	9.682%	$240.061	$240.06	$240.05	$240.10
Purchase #6	$41.40	5.477%	$43.6675	$43.67	$43.65	$43.70
Purchase #7	$69.77	9.480%	$76.3842	$76.38	$76.40	$76.40
7 purchase totals =	$810.25		$879.0269	$879.03	$879.00	$879.10