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	$238.83	13.229%	$270.4248	$270.42	$270.40	$270.40
Purchase #2	$52.73	8.714%	$57.3249	$57.32	$57.30	$57.30
Purchase #3	$49.70	7.179%	$53.268	$53.27	$53.25	$53.30
Purchase #4	$204.38	9.410%	$223.6122	$223.61	$223.60	$223.60
Purchase #5	$111.89	10.401%	$123.5277	$123.53	$123.55	$123.50
Purchase #6	$223.46	6.271%	$237.4732	$237.47	$237.45	$237.50
Purchase #7	$88.92	6.592%	$94.7816	$94.78	$94.80	$94.80
7 purchase totals =	$969.91		$1,060.4124	$1,060.40	$1,060.35	$1,060.40