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	$129.58	5.370%	$136.5384	$136.54	$136.55	$136.50
Purchase #2	$92.87	6.711%	$99.1025	$99.10	$99.10	$99.10
Purchase #3	$18.42	10.382%	$20.3324	$20.33	$20.35	$20.30
Purchase #4	$49.85	3.116%	$51.4033	$51.40	$51.40	$51.40
Purchase #5	$131.65	9.486%	$144.1383	$144.14	$144.15	$144.10
Purchase #6	$201.70	7.281%	$216.3858	$216.39	$216.40	$216.40
Purchase #7	$161.72	12.516%	$181.9609	$181.96	$181.95	$182.00
7 purchase totals =	$785.79		$849.8616	$849.86	$849.90	$849.80