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	$131.57	8.290%	$142.4772	$142.48	$142.50	$142.50
Purchase #2	$134.32	12.828%	$151.5506	$151.55	$151.55	$151.60
Purchase #3	$37.88	5.551%	$39.9827	$39.98	$40.00	$40.00
Purchase #4	$117.77	11.438%	$131.2405	$131.24	$131.25	$131.20
Purchase #5	$146.65	13.315%	$166.1764	$166.18	$166.20	$166.20
Purchase #6	$127.39	7.518%	$136.9672	$136.97	$136.95	$137.00
Purchase #7	$29.37	9.863%	$32.2668	$32.27	$32.25	$32.30
7 purchase totals =	$724.95		$800.6614	$800.67	$800.70	$800.80