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	$18.44	9.688%	$20.2265	$20.23	$20.25	$20.20
Purchase #2	$46.71	10.713%	$51.714	$51.71	$51.70	$51.70
Purchase #3	$249.28	12.716%	$280.9784	$280.98	$281.00	$281.00
Purchase #4	$52.69	13.652%	$59.8832	$59.88	$59.90	$59.90
Purchase #5	$152.63	10.459%	$168.5936	$168.59	$168.60	$168.60
Purchase #6	$89.79	5.565%	$94.7868	$94.79	$94.80	$94.80
Purchase #7	$55.71	12.512%	$62.6804	$62.68	$62.70	$62.70
7 purchase totals =	$665.25		$738.8629	$738.86	$738.95	$738.90