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	$240.34	6.293%	$255.4646	$255.46	$255.45	$255.50
Purchase #2	$71.80	11.775%	$80.2545	$80.25	$80.25	$80.30
Purchase #3	$46.54	6.532%	$49.58	$49.58	$49.60	$49.60
Purchase #4	$234.93	9.682%	$257.6759	$257.68	$257.70	$257.70
Purchase #5	$225.64	7.187%	$241.8567	$241.86	$241.85	$241.90
Purchase #6	$72.33	8.630%	$78.5721	$78.57	$78.55	$78.60
Purchase #7	$78.64	11.780%	$87.9038	$87.90	$87.90	$87.90
7 purchase totals =	$970.22		$1,051.3076	$1,051.30	$1,051.30	$1,051.50