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	$17.50	6.680%	$18.669	$18.67	$18.65	$18.70
Purchase #2	$90.78	7.471%	$97.5622	$97.56	$97.55	$97.60
Purchase #3	$240.55	8.505%	$261.0088	$261.01	$261.00	$261.00
Purchase #4	$152.79	7.543%	$164.3149	$164.31	$164.30	$164.30
Purchase #5	$128.58	3.827%	$133.5008	$133.50	$133.50	$133.50
Purchase #6	$191.88	7.633%	$206.5262	$206.53	$206.55	$206.50
Purchase #7	$85.35	13.807%	$97.1343	$97.13	$97.15	$97.10
7 purchase totals =	$907.43		$978.7162	$978.71	$978.70	$978.70