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	$70.35	12.853%	$79.3921	$79.39	$79.40	$79.40
Purchase #2	$102.86	13.214%	$116.4519	$116.45	$116.45	$116.50
Purchase #3	$130.78	9.803%	$143.6004	$143.60	$143.60	$143.60
Purchase #4	$156.42	9.473%	$171.2377	$171.24	$171.25	$171.20
Purchase #5	$227.73	8.205%	$246.4152	$246.42	$246.40	$246.40
Purchase #6	$71.50	9.656%	$78.404	$78.40	$78.40	$78.40
Purchase #7	$169.92	12.529%	$191.2093	$191.21	$191.20	$191.20
7 purchase totals =	$929.56		$1,026.7106	$1,026.71	$1,026.70	$1,026.70