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	$136.65	9.845%	$150.1032	$150.10	$150.10	$150.10
Purchase #2	$127.27	6.316%	$135.3084	$135.31	$135.30	$135.30
Purchase #3	$142.98	8.775%	$155.5265	$155.53	$155.55	$155.50
Purchase #4	$201.78	10.672%	$223.314	$223.31	$223.30	$223.30
Purchase #5	$51.35	3.379%	$53.0851	$53.09	$53.10	$53.10
Purchase #6	$102.97	9.111%	$112.3516	$112.35	$112.35	$112.40
Purchase #7	$66.86	8.406%	$72.4803	$72.48	$72.50	$72.50
7 purchase totals =	$829.86		$902.1691	$902.17	$902.20	$902.20