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	$107.25	10.733%	$118.7611	$118.76	$118.75	$118.80
Purchase #2	$158.73	4.854%	$166.4348	$166.43	$166.45	$166.40
Purchase #3	$220.34	7.349%	$236.5328	$236.53	$236.55	$236.50
Purchase #4	$35.58	10.832%	$39.434	$39.43	$39.45	$39.40
Purchase #5	$31.36	4.353%	$32.7251	$32.73	$32.75	$32.70
Purchase #6	$29.42	11.809%	$32.8942	$32.89	$32.90	$32.90
Purchase #7	$147.35	11.482%	$164.2687	$164.27	$164.25	$164.30
7 purchase totals =	$730.03		$791.0507	$791.04	$791.10	$791.00