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	$179.40	4.209%	$186.9509	$186.95	$186.95	$187.00
Purchase #2	$220.91	11.226%	$245.7094	$245.71	$245.70	$245.70
Purchase #3	$52.93	13.202%	$59.9178	$59.92	$59.90	$59.90
Purchase #4	$85.26	5.404%	$89.8675	$89.87	$89.85	$89.90
Purchase #5	$117.92	8.136%	$127.514	$127.51	$127.50	$127.50
Purchase #6	$132.46	11.383%	$147.5379	$147.54	$147.55	$147.50
Purchase #7	$39.48	13.261%	$44.7154	$44.72	$44.70	$44.70
7 purchase totals =	$828.36		$902.2129	$902.22	$902.15	$902.20