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	$229.29	6.130%	$243.3455	$243.35	$243.35	$243.30
Purchase #2	$110.36	12.116%	$123.7312	$123.73	$123.75	$123.70
Purchase #3	$162.71	4.343%	$169.7765	$169.78	$169.80	$169.80
Purchase #4	$248.82	12.865%	$280.8307	$280.83	$280.85	$280.80
Purchase #5	$200.90	6.835%	$214.6315	$214.63	$214.65	$214.60
Purchase #6	$126.54	8.383%	$137.1478	$137.15	$137.15	$137.10
Purchase #7	$66.45	7.324%	$71.3168	$71.32	$71.30	$71.30
7 purchase totals =	$1,145.07		$1,240.7800	$1,240.79	$1,240.85	$1,240.60