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	$38.68	4.675%	$40.4883	$40.49	$40.50	$40.50
Purchase #2	$194.65	12.418%	$218.8216	$218.82	$218.80	$218.80
Purchase #3	$51.35	11.703%	$57.3595	$57.36	$57.35	$57.40
Purchase #4	$250.90	11.812%	$280.5363	$280.54	$280.55	$280.50
Purchase #5	$181.56	10.337%	$200.3279	$200.33	$200.35	$200.30
Purchase #6	$58.87	9.126%	$64.2425	$64.24	$64.25	$64.20
Purchase #7	$216.45	12.188%	$242.8309	$242.83	$242.85	$242.80
7 purchase totals =	$992.46		$1,104.6070	$1,104.61	$1,104.65	$1,104.50