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	$231.80	3.554%	$240.0382	$240.04	$240.05	$240.00
Purchase #2	$236.60	3.129%	$244.0032	$244.00	$244.00	$244.00
Purchase #3	$80.89	10.710%	$89.5533	$89.55	$89.55	$89.60
Purchase #4	$93.48	5.155%	$98.2989	$98.30	$98.30	$98.30
Purchase #5	$79.65	12.512%	$89.6158	$89.62	$89.60	$89.60
Purchase #6	$196.31	8.584%	$213.1613	$213.16	$213.15	$213.20
Purchase #7	$99.93	5.421%	$105.3472	$105.35	$105.35	$105.30
7 purchase totals =	$1,018.66		$1,080.0179	$1,080.02	$1,080.00	$1,080.00