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	$177.94	6.429%	$189.3798	$189.38	$189.40	$189.40
Purchase #2	$140.85	11.407%	$156.9168	$156.92	$156.90	$156.90
Purchase #3	$103.90	5.262%	$109.3672	$109.37	$109.35	$109.40
Purchase #4	$190.53	9.574%	$208.7713	$208.77	$208.75	$208.80
Purchase #5	$237.67	9.438%	$260.1013	$260.10	$260.10	$260.10
Purchase #6	$105.31	12.570%	$118.5475	$118.55	$118.55	$118.50
Purchase #7	$135.73	11.579%	$151.4462	$151.45	$151.45	$151.40
7 purchase totals =	$1,091.93		$1,194.5301	$1,194.54	$1,194.50	$1,194.50