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	$90.37	3.419%	$93.4598	$93.46	$93.45	$93.50
Purchase #2	$172.25	5.698%	$182.0648	$182.06	$182.05	$182.10
Purchase #3	$126.53	8.565%	$137.3673	$137.37	$137.35	$137.40
Purchase #4	$250.63	5.324%	$263.9735	$263.97	$263.95	$264.00
Purchase #5	$43.41	7.777%	$46.786	$46.79	$46.80	$46.80
Purchase #6	$153.70	9.695%	$168.6012	$168.60	$168.60	$168.60
Purchase #7	$99.47	12.211%	$111.6163	$111.62	$111.60	$111.60
7 purchase totals =	$936.36		$1,003.8689	$1,003.87	$1,003.80	$1,004.00