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	$243.39	11.287%	$270.8614	$270.86	$270.85	$270.90
Purchase #2	$68.75	6.497%	$73.2167	$73.22	$73.20	$73.20
Purchase #3	$123.72	13.615%	$140.5645	$140.56	$140.55	$140.60
Purchase #4	$139.41	4.322%	$145.4353	$145.44	$145.45	$145.40
Purchase #5	$143.37	9.153%	$156.4927	$156.49	$156.50	$156.50
Purchase #6	$21.62	4.179%	$22.5235	$22.52	$22.50	$22.50
Purchase #7	$216.42	4.664%	$226.5138	$226.51	$226.50	$226.50
7 purchase totals =	$956.68		$1,035.6079	$1,035.60	$1,035.55	$1,035.60