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	$123.86	12.870%	$139.8008	$139.80	$139.80	$139.80
Purchase #2	$53.63	6.835%	$57.2956	$57.30	$57.30	$57.30
Purchase #3	$230.35	4.415%	$240.52	$240.52	$240.50	$240.50
Purchase #4	$211.90	3.305%	$218.9033	$218.90	$218.90	$218.90
Purchase #5	$51.56	6.704%	$55.0166	$55.02	$55.00	$55.00
Purchase #6	$61.67	5.155%	$64.8491	$64.85	$64.85	$64.80
Purchase #7	$144.37	13.258%	$163.5106	$163.51	$163.50	$163.50
7 purchase totals =	$877.34		$939.8960	$939.90	$939.85	$939.80