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	$249.56	9.856%	$274.1566	$274.16	$274.15	$274.20
Purchase #2	$183.30	7.142%	$196.3913	$196.39	$196.40	$196.40
Purchase #3	$20.38	3.375%	$21.0678	$21.07	$21.05	$21.10
Purchase #4	$40.43	6.833%	$43.1926	$43.19	$43.20	$43.20
Purchase #5	$250.60	9.265%	$273.8181	$273.82	$273.80	$273.80
Purchase #6	$196.51	10.121%	$216.3988	$216.40	$216.40	$216.40
Purchase #7	$18.75	13.145%	$21.2147	$21.21	$21.20	$21.20
7 purchase totals =	$959.53		$1,046.2399	$1,046.24	$1,046.20	$1,046.30