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	$37.27	5.705%	$39.3963	$39.40	$39.40	$39.40
Purchase #2	$11.89	9.650%	$13.0374	$13.04	$13.05	$13.00
Purchase #3	$114.68	11.125%	$127.4382	$127.44	$127.45	$127.40
Purchase #4	$182.94	7.663%	$196.9587	$196.96	$196.95	$197.00
Purchase #5	$118.70	5.119%	$124.7763	$124.78	$124.80	$124.80
Purchase #6	$94.90	7.708%	$102.2149	$102.21	$102.20	$102.20
Purchase #7	$167.71	10.380%	$185.1183	$185.12	$185.10	$185.10
7 purchase totals =	$728.09		$788.9401	$788.95	$788.95	$788.90