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	$28.93	11.329%	$32.2075	$32.21	$32.20	$32.20
Purchase #2	$35.76	7.517%	$38.4481	$38.45	$38.45	$38.40
Purchase #3	$187.34	11.671%	$209.2045	$209.20	$209.20	$209.20
Purchase #4	$247.45	13.341%	$280.4623	$280.46	$280.45	$280.50
Purchase #5	$7.25	4.752%	$7.5945	$7.59	$7.60	$7.60
Purchase #6	$61.60	5.559%	$65.0243	$65.02	$65.00	$65.00
Purchase #7	$86.62	3.106%	$89.3104	$89.31	$89.30	$89.30
7 purchase totals =	$654.95		$722.2516	$722.24	$722.20	$722.20