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	$37.78	13.680%	$42.9483	$42.95	$42.95	$42.90
Purchase #2	$231.94	3.694%	$240.5079	$240.51	$240.50	$240.50
Purchase #3	$76.95	7.354%	$82.6089	$82.61	$82.60	$82.60
Purchase #4	$248.95	12.596%	$280.3077	$280.31	$280.30	$280.30
Purchase #5	$243.27	4.586%	$254.4264	$254.43	$254.45	$254.40
Purchase #6	$197.54	3.259%	$203.9778	$203.98	$204.00	$204.00
Purchase #7	$48.61	6.756%	$51.8941	$51.89	$51.90	$51.90
7 purchase totals =	$1,085.04		$1,156.6711	$1,156.68	$1,156.70	$1,156.60