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	$84.60	13.723%	$96.2097	$96.21	$96.20	$96.20
Purchase #2	$66.47	7.263%	$71.2977	$71.30	$71.30	$71.30
Purchase #3	$140.46	11.366%	$156.4247	$156.42	$156.40	$156.40
Purchase #4	$215.95	6.237%	$229.4188	$229.42	$229.40	$229.40
Purchase #5	$23.32	8.527%	$25.3085	$25.31	$25.30	$25.30
Purchase #6	$179.92	11.475%	$200.5658	$200.57	$200.55	$200.60
Purchase #7	$227.60	9.544%	$249.3221	$249.32	$249.30	$249.30
7 purchase totals =	$938.32		$1,028.5473	$1,028.55	$1,028.45	$1,028.50