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	$38.41	9.534%	$42.072	$42.07	$42.05	$42.10
Purchase #2	$164.26	12.636%	$185.0159	$185.02	$185.00	$185.00
Purchase #3	$137.51	7.191%	$147.3983	$147.40	$147.40	$147.40
Purchase #4	$94.51	6.139%	$100.312	$100.31	$100.30	$100.30
Purchase #5	$67.25	5.309%	$70.8203	$70.82	$70.80	$70.80
Purchase #6	$104.93	7.235%	$112.5217	$112.52	$112.50	$112.50
Purchase #7	$116.72	9.853%	$128.2204	$128.22	$128.20	$128.20
7 purchase totals =	$723.59		$786.3606	$786.36	$786.25	$786.30