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	$42.52	6.514%	$45.2898	$45.29	$45.30	$45.30
Purchase #2	$127.73	9.616%	$140.0125	$140.01	$140.00	$140.00
Purchase #3	$13.25	11.523%	$14.7768	$14.78	$14.80	$14.80
Purchase #4	$124.85	7.858%	$134.6607	$134.66	$134.65	$134.70
Purchase #5	$80.97	11.384%	$90.1876	$90.19	$90.20	$90.20
Purchase #6	$147.50	11.491%	$164.4492	$164.45	$164.45	$164.40
Purchase #7	$216.81	13.434%	$245.9363	$245.94	$245.95	$245.90
7 purchase totals =	$753.63		$835.3129	$835.32	$835.35	$835.30