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	$11.68	6.864%	$12.4817	$12.48	$12.50	$12.50
Purchase #2	$58.67	11.691%	$65.5291	$65.53	$65.55	$65.50
Purchase #3	$67.82	10.796%	$75.1418	$75.14	$75.15	$75.10
Purchase #4	$129.52	10.457%	$143.0639	$143.06	$143.05	$143.10
Purchase #5	$69.98	12.409%	$78.6638	$78.66	$78.65	$78.70
Purchase #6	$187.54	4.643%	$196.2475	$196.25	$196.25	$196.20
Purchase #7	$248.71	4.349%	$259.5264	$259.53	$259.55	$259.50
7 purchase totals =	$773.92		$830.6542	$830.65	$830.70	$830.60