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	$154.59	3.500%	$160.0007	$160.00	$160.00	$160.00
Purchase #2	$169.56	11.185%	$188.5253	$188.53	$188.55	$188.50
Purchase #3	$179.58	5.815%	$190.0226	$190.02	$190.00	$190.00
Purchase #4	$92.61	5.384%	$97.5961	$97.60	$97.60	$97.60
Purchase #5	$218.83	4.682%	$229.0756	$229.08	$229.10	$229.10
Purchase #6	$80.63	9.791%	$88.5245	$88.52	$88.50	$88.50
Purchase #7	$119.62	11.243%	$133.0689	$133.07	$133.05	$133.10
7 purchase totals =	$1,015.42		$1,086.8137	$1,086.82	$1,086.80	$1,086.80