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	$233.99	9.134%	$255.3626	$255.36	$255.35	$255.40
Purchase #2	$248.69	12.767%	$280.4403	$280.44	$280.45	$280.40
Purchase #3	$243.51	8.709%	$264.7173	$264.72	$264.70	$264.70
Purchase #4	$164.82	11.432%	$183.6622	$183.66	$183.65	$183.70
Purchase #5	$40.25	12.785%	$45.396	$45.40	$45.40	$45.40
Purchase #6	$114.35	4.869%	$119.9177	$119.92	$119.90	$119.90
Purchase #7	$73.54	12.652%	$82.8443	$82.84	$82.85	$82.80
7 purchase totals =	$1,119.15		$1,232.3404	$1,232.34	$1,232.30	$1,232.30