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	$208.87	12.261%	$234.4796	$234.48	$234.50	$234.50
Purchase #2	$38.54	10.475%	$42.5771	$42.58	$42.60	$42.60
Purchase #3	$50.63	4.809%	$53.0648	$53.06	$53.05	$53.10
Purchase #4	$76.41	7.422%	$82.0812	$82.08	$82.10	$82.10
Purchase #5	$29.96	10.507%	$33.1079	$33.11	$33.10	$33.10
Purchase #6	$29.66	9.510%	$32.4807	$32.48	$32.50	$32.50
Purchase #7	$72.90	7.274%	$78.2027	$78.20	$78.20	$78.20
7 purchase totals =	$506.97		$555.9940	$555.99	$556.05	$556.10