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	$112.57	13.524%	$127.794	$127.79	$127.80	$127.80
Purchase #2	$78.84	5.709%	$83.341	$83.34	$83.35	$83.30
Purchase #3	$127.90	10.517%	$141.3512	$141.35	$141.35	$141.40
Purchase #4	$79.99	9.235%	$87.3771	$87.38	$87.40	$87.40
Purchase #5	$121.43	8.107%	$131.2743	$131.27	$131.25	$131.30
Purchase #6	$120.27	7.571%	$129.3756	$129.38	$129.40	$129.40
Purchase #7	$106.78	7.603%	$114.8985	$114.90	$114.90	$114.90
7 purchase totals =	$747.78		$815.4117	$815.41	$815.45	$815.50