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	$122.38	11.601%	$136.5773	$136.58	$136.60	$136.60
Purchase #2	$59.29	12.839%	$66.9022	$66.90	$66.90	$66.90
Purchase #3	$172.31	8.835%	$187.5336	$187.53	$187.55	$187.50
Purchase #4	$201.32	13.499%	$228.4962	$228.50	$228.50	$228.50
Purchase #5	$43.76	11.774%	$48.9123	$48.91	$48.90	$48.90
Purchase #6	$81.77	8.872%	$89.0246	$89.02	$89.00	$89.00
Purchase #7	$216.59	9.432%	$237.0188	$237.02	$237.00	$237.00
7 purchase totals =	$897.42		$994.4650	$994.46	$994.45	$994.40