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	$238.86	12.691%	$269.1737	$269.17	$269.15	$269.20
Purchase #2	$223.35	11.816%	$249.741	$249.74	$249.75	$249.70
Purchase #3	$83.37	8.238%	$90.238	$90.24	$90.25	$90.20
Purchase #4	$30.41	12.304%	$34.1516	$34.15	$34.15	$34.20
Purchase #5	$18.95	13.707%	$21.5475	$21.55	$21.55	$21.50
Purchase #6	$127.43	12.872%	$143.8328	$143.83	$143.85	$143.80
Purchase #7	$174.64	6.541%	$186.0632	$186.06	$186.05	$186.10
7 purchase totals =	$897.01		$994.7478	$994.74	$994.75	$994.70