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	$105.38	3.577%	$109.1494	$109.15	$109.15	$109.10
Purchase #2	$106.45	13.645%	$120.9751	$120.98	$121.00	$121.00
Purchase #3	$174.91	3.733%	$181.4394	$181.44	$181.45	$181.40
Purchase #4	$136.51	13.480%	$154.9115	$154.91	$154.90	$154.90
Purchase #5	$118.41	11.183%	$131.6518	$131.65	$131.65	$131.70
Purchase #6	$246.45	11.738%	$275.3783	$275.38	$275.40	$275.40
Purchase #7	$155.90	5.447%	$164.3919	$164.39	$164.40	$164.40
7 purchase totals =	$1,044.01		$1,137.8974	$1,137.90	$1,137.95	$1,137.90