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	$102.43	9.730%	$112.3964	$112.40	$112.40	$112.40
Purchase #2	$187.32	12.596%	$210.9148	$210.91	$210.90	$210.90
Purchase #3	$116.53	9.141%	$127.182	$127.18	$127.20	$127.20
Purchase #4	$115.61	10.157%	$127.3525	$127.35	$127.35	$127.40
Purchase #5	$219.39	13.850%	$249.7755	$249.78	$249.80	$249.80
Purchase #6	$176.93	4.189%	$184.3416	$184.34	$184.35	$184.30
Purchase #7	$77.52	8.817%	$84.3549	$84.35	$84.35	$84.40
7 purchase totals =	$995.73		$1,096.3177	$1,096.31	$1,096.35	$1,096.40